Robert Jones

Many tools have been developed to aid law enforcement personnel. These include fingerprinting, blood typing, lie detecting and DNA (desoxyribonucleic acid) analysis. The latter, especially, has undergone continuing improvements and is now an established forensic tool. Its use has been spreading to law enforcement agencies throughout the world. Even a problem of needing a sizeable sample of a substance containing DNA for analysis has been solved by a Nobel-Prize-winning discovery of means for amplifying (replicating) quite small (even degraded) amounts of DNA. DNA is found in every nucleated cell in our bodies, and it is the same in every such cell. DNA analysis, sometimes referred to as DNA profiling or DNA fingerprinting, is basically a process that compares the genetic makeup of a small number of DNA segments in testable samples to reveal their presence or absence. There are a number of techniques used, and those that are least accurate are still capable of excluding innocent suspects. In the sense of this discussion, the success of DNA analysis is to be considered a first forensic PING.

Just as it appeared that DNA analysis was becoming regarded as a forensic gold standard, however, a nasty dose of aqua regia* (so called because it is sufficiently corrosive to dissolve “royal” metals such as gold and platinum) showered down upon it. Scientists dribbled the representative first drop of the shower by simply separating red and white blood cells and plasma in a female donor’s blood. Next, they took DNA from a male donor and added it to the female’s red blood cells, which contain no DNA. This created blood that contained only the DNA of the male. To test the deception, a sample was sent for profiling to a laboratory used by the FBI, where the resulting profile raised not one eyebrow. More drops were dribbled by fabricating saliva. Bucketfuls of aqua regia were dumped when scientists revealed that, if they had a DNA profile of a person, they could construct DNA to match it without having any tissue at all from that person. One could then plant the DNA at a crime scene to incriminate an innocent person. Just imagine what defense attorneys could do with that information. In the new sense of this discussion, the corroding of the forensic DNA gold standard may be considered a first forensic PONG.

Just when it appeared that the forensic DNA gold standard faced dissolution, a niobium umbrella descended to protect the gold standard from the aqua regia shower. This represented a development by scientists of a method that detected fabricated DNA. The method is based on the fact that amplified (replicated) DNA is not methylated (does not have certain molecules attached at specific points to the DNA). In the more recent sense of this discussion, the ability (represented by the niobium umbrella) to protect the forensic gold standard by performing a test for the presence or absence of methylation may be considered a second forensic PING.

Just as the forensic gold standard was apparently being restored, however, the niobium umbrella representing the method of detecting fabricated DNA was doused by concentrated sulfuric acid, which promptly began redissolving it. It was made public that any competent molecular biologist would know how to use a simple treatment** to methylate amplified DNA. This, of course, would severely reduce the usefulness of the methylation test. If this is true, such a treatment could certainly be considered a second forensic PONG.

Fortunately, DNA evidence is not the only type of evidence considered in investigations and trials.

Extra facts:

* Aqua regia, as we might recall from our chemistry classes, is an acid comprising a mixture of one part (by volume) concentrated nitric acid and three parts concentrated hydrochloric acid.

** For those biochemists among us, the simple treatment referred to is a CpG methyltransferase treatment, CpG standing for cytosine and quanine (no, not quinine) separated by a phosphate that links the two nucleosides in DNA.

The foregoing will not appear on the final exam.

4. The source of the name “Jack the Ripper” was a letter written a few days before Catherine’s death.: It was received Sept. 27, 1888 at the Central News Agency. One sentence read, “The next job I do I shall clip the lady’s ears off and send to the police officers just for jolly wouldn’t you.” The letter was signed “Yours truly, Jack the Ripper.” The fourth victim, Catherine, was killed just three days later; and a portion of an earlobe had been removed. Also removed had been her left kidney, the upper portion of her uterus, and a length of intestine. The letter was the first written that mentioned the name, “Jack the Ripper.” A copy of the letter follows:

Dear Boss,

I keep on hearing the police have caught me but they wont fix me just yet. I have laughed when they look so clever and talk about being on the right track. That joke about Leather Apron gave me real fits. I am down on whores and I shant quit ripping them till I do get buckled. Grand work the last job was. I gave the lady no time to squeal. How can they catch me now. I love my work and want to start again. You will soon hear of me with my funny little games. I saved some of the proper red stuff in a ginger beer bottle over the last job to write with but it went thick like glue and I cant use it. Red ink is fit enough I hope ha. ha. The next job I do I shall clip the ladys ears off and send to the police officers just for jolly wouldn’t you. Keep this letter back till I do a bit more work, then give it out straight. My knife’s so nice and sharp I want to get to work right away if I get a chance. Good Luck.

Yours truly

Jack the Ripper

Don’t mind me giving the trade name

PS Wasnt good enough to post this before I got all the red ink off my hands curse it No luck yet. They say I’m a doctor now. ha ha

FORENSICS 112: OUCHES, LARGE AND SMALL

(Part 2)

There were no words to describe the dry heat. The sky was cloudless, and air above the parched earth shimmered under a merciless Sun. The remains of a river lay in but a few shallow pools. Local animals were forced to share what little was left, and many did not take kindly to such foreign behavior. As water gradually disappeared, dead bodies began to litter the area. Still-living animals fed on the dead and smaller live animals. Eventually, the large animals were forced to eat each other, even others of their own species. The last one finally died, and its bones joined others scattered about the dried pool.

When I mentioned that there were no words to describe the dry heat, I meant it literally. The scene took place on the island of Madagascar some 65 million years ago, and there weren’t many humans around back then to voice any words. The last animal to die was a majungasaurus. It would have been at least 26 feet long, weighed 2400 pounds, and been the apex predator on the island. Fossilized bones of it and others like it bore tooth marks that had been engraved as flesh was torn from the bones and devoured. Some tooth marks on majungasaurus bones were identified as being made by teeth belonging to other animals of the same species, which indicated that they had cannibalized each other. That is an interesting fact, but many other creatures – including lions, tigers, bears, chimpanzees, hamsters, squirrels, birds, spiders, rats and bats – eat members of their own species, even members of their own families. The relevance of the dinosaur business to forensics has to do with the fact that bite marks – even those found on fossilized bones – can be matched to those of animals that did the biting.

The field of studying bite marks possibly connected to a crime is known as forensic odontology. Human teeth are usually not thought of as being weapons, but their marks have been found on a surprising number of physical assault victims. As a matter of fact, they appear, as defense wounds, on a fair number of attackers as well. Bite marks have been found on nearly every location on a human body. Females are most often bitten on breasts and legs during sexual attacks, and men suffer bites most often on arms and shoulders. Defensive wounds most often appear on arms and hands.

Beginning from the front center and proceeding rearward along one side, adult human teeth include a central incisor, a lateral incisor, a cuspid (commonly referred to as a canine), two bicuspids (premolars), two molars and sometimes a third molar (commonly referred to as a wisdom tooth). Upper teeth form what is known as a maxillary arch, or arcade; and lower teeth form what is known as a mandibular arch, or arcade. Bites can result in a wide range of wounds including bruises, scrapes, cuts, lacerations and avulsives. An avulsive bite is one that tears away flesh. A previously mentioned majungasaurus could easily inflict many such bites on a large scale, and a person can also, but on a somewhat smaller scale. Bite marks can be ring shaped or be formed like a pair of spaced-apart, U-shaped arches. Bite mark characteristics fall into two basic categories, namely, class characteristics and individual characteristics. Class characteristics identify the group sharing them, such as humans, animals, fish, etc. For example, a bite mark having four relatively linear or rectangular contusions (bruises) is a class characteristic of human incisors.

Individual characteristics identify individual variations; and there are two types, namely, arch characteristics and dental characteristics. Arch characteristics refer to the arrangement of teeth within a bite mark. These might include a combination of misaligned or rotated teeth or of separated teeth that could distinguish one individual from another. Dental characteristics refer to features, such as uncommon wear, chips or fractures, of individual teeth.

Even when teeth are not used to bite another person, bite marks can provide important forensic information. Chewing gum or food such as cheese, apples, melons and, of course, Janet’s favorite, chocolate, left at a crime scene can preserve dental impressions from which casts can be made. The casts can then duplicate at least portions of the teeth that made the impressions and can be compared to casts made of a suspect’s teeth. Depending on the condition of a bite mark on flesh, an impression might be taken of it also. A cast could then be made that would capture not only the bite mark but also a victim’s body contours.

Teeth can be long, short, narrow, wide, thick, thin, buck, spaced and crooked. Incisors tend to create rectangular wounds, and cuspids (often referred to as canines), triangular wounds. Individual arrangements of teeth owe much to their eruption sequence (teeth do not erupt

simultaneously) of anterior (front) and posterior (back) teeth. Cuspids (canines) have to wedge themselves into a dental arch between teeth that erupted before them, and this often causes displacement and rotation of adjoining teeth. Incisors are the teeth that are most affected by crowding.

During their existence, teeth can be subject to what are referred to as accidental or individual traits including congenital malformations, rotations, fractures and, of course, wear. All the foregoing factors contribute to creating bite marks that are relatively unique. Just how unique is still being debated. Some progress has been made in standardizing comparison procedures, but determinations often depend on an expert’s experience and judgment.

There are pitfalls in depending exclusively on bite-mark evidence for convictions. In 1991, a Phoenix cocktail waitress was found dead, the victim of eleven stab wounds, a bite on her breast made through a tank top and another bite on her neck. There was very little evidence, but an Arizona State dental expert testified that bite marks on the victim’s breast matched the teeth of one Ray Krone, who soon became known as the “snaggletooth killer.” Krone was sentenced to death and spent several years on death row. In a subsequent retrial, he was sentenced to life imprisonment. After spending a decade in jail, Krone was released when a DNA test proved that saliva from the victim’s tank top did not match his. DNA not only cleared Krone but implicated another man already serving a term in prison for attempted child abuse.

Especially with surviving victims, but also with dead victims, the sharpness of bite mark evidence, and its forensic value, gradually decreases over time. It is thus important to record the evidence as soon as possible. Photographing a bite mark preserves a visual image that, if done properly, can be later compared to other dental evidence. A reference scale, such as a ruler, is placed next to, and in the same plane as, the mark so that accurate measurements of mark details can be made. A camera is positioned with its lens pointed at right angles to the plane of the mark to avoid perspective distortion. Even when great care is taken, a comparative analysis is not an easy task due to the fact that skin is curved, is easily distorted and is often undergoing edema (swelling). Illuminating a wound site with different colored lights often brings out details not evident when exposed to normal light. In fact, finding a faint bite mark can be greatly facilitated by using an ultraviolet light. A bite wound is accompanied by saliva, and human saliva glows brightly in ultraviolet light. A variety of photographic filters are also sometimes used to enhance photographs.

It sounds obvious, but an investigator must make certain a wound being analyzed is actually a bite mark. Forceful contacts with certain circular or elliptical objects, or even some burns, can appear to be bite marks. A lack of class characteristics such as the rectangular and triangular wounds made by individual teeth as mentioned previously will, however, disqualify them. An investigator must also be careful to check an individual’s teeth if there exists a possibility that a bite might have been self-inflicted.

Since biting and sucking deposit saliva on skin, DNA is often retrievable from a bite or suction wound. A simple procedure involves using a first cotton swab to wash the area contacted by tongue and lips with sterile distilled water. A second, dry swab is then used to collect moisture left by the first swab. Both swabs are air dried at room temperature for at least 45 minutes and are then placed in a sterile paper evidence envelope or box that will allow some air circulation. They are not to be sealed in plastic bags or containers. (I seem to recall seeing TV crime scene investigators plunking swabs into what appeared to be small plastic bottles.) The swabs should be kept at room temperature if they are to be submitted for analysis within six hours or refrigerated if they are to be stored for a longer period. A sample of a victim’s blood or tissue is also usually taken for DNA comparison with that from the swabs.

Extra facts:

Male teeth are usually somewhat larger than female teeth, but the difference is usually insufficient to guarantee accurate sex identification from them or their bite marks.

Human bites are more likely to become infected than are animal bites. Errol Flynn wrote that a neglected wound he had received when he punched someone in the mouth almost resulted in a loss of his hand.

Cannibalizing animals are not only common, they can also be impatient. Some can’t even wait until they’re born. Sand tiger sharks have two uteruses, and their embryos develop teeth. Only the largest embryo in each will survive to be born. Guess what happens to the smaller ones.

Assaults of all kinds can result in body wounds, and most involve skin damage. Our skin just seems to hang around not doing much, but it performs some very important functions. It stands between us and many harmful agents. It also plays important roles in maintaining our body temperature and in gathering sensory information from our surroundings.Skin comprises an outermost layer known as an epidermis. Its thickness ranges from 0.05 mm eyelids to 1.5 mm palms and soles, and pigment (melanin) is produced within it. Cells of the innermost of its five sublayers divide and push previously formed cells upward, where they gradually flatten, die and slough off.

Below the epidermis is a dermis layer. It provides a home for capillaries and nerves, the nerves transmitting touch, pressure, pain, itch and temperature sensations. Also within the dermis are sweat glands and hair follicles. Oil (sebaceous) glands and odor glands also reside there and are associated with the hair follicles. Below the dermis is a subcutaneous (hypodermis) layer, which connects the skin to whatever is below it. It contains a layer of fat (at least some in every one of us) and blood vessels that supply and drain the capillaries in the dermis.

An examination of body wounds can provide valuable information relating to the manner of a person’s death and to the contribution each made toward that death. Photographs of wounds and a nearby, readable measuring device provide means for later estimating wound dimensions. Of obvious additional importance is a report accurately describing the wounds and their locations with respect, for example, to how far left or right they are of the body’s midline, how far below certain vertebrae and how far above the ground they are. The distance above ground can, of course, be one factor in identifying a make and model of vehicle that struck a victim.

Wounds can generally be forensically defined as tissue damage resulting from being shot, stabbed, struck, strangled, or bitten by someone, from being struck by a vehicle, from having fallen, or from having lit a dynamite fuse that was a tad too short. Wounds can also be generally categorized as being abrasions, bruises, contusions, incised wounds or lacerations; and it is common for a body to display more than one type of wound. This essay addresses the first two types.

An abrasion is what most persons would refer to as a “scratch.” It is a superficial injury; and, since its damage is generally limited to the top skin layer (epidermis), it rarely bleeds much, if at all. Active children often display abrasions on their knees and elbows. Wounding forces that cause abrasions act primarily along the surface of skin rather than toward it. If substantial force is directed toward the skin, the resulting wound is referred to as a “crush” injury. Toppled motorcycle riders often suffer abrasions on various parts of their hides while using those parts as brake pads as they skid to a stop. Many of us have experienced what is known as a rope or friction burn when a rope slides quickly through our hands. A hurrying dental technician whipping a piece of dental floss from between one’s teeth can burn one’s gum in a similar manner. (Are you dental technicians out there paying attention to this?)

Just as snow is piled at one end of a run by a snow plow, dislodged epidermis is piled at the terminal end of an abrasion. This indicates the direction of the causing force. Jagged edges of the abrasion can also point in the direction of force. Of even greater consequence, abrasions sometimes preserve, for example, images of items that created them; and photographs of the images can be compared later to vehicle bumpers, grilles, hood ornaments and the like.

A closed wound known as a bruise, or contusion, refers to an area of hemorrhage that suffered a leakage of blood from blood vessels at the capillary level into surrounding tissues. Types of bruises include petechial hemorrhages, which involve pinpoint marks where blood extravasates (escapes) from vessels. Such can be caused by blunt trauma, pressure to the neck or chest, or simply by violent coughing, sneezing or even suction (as with a hickey).

An extravasation of blood within the dermis but below the capillaries, causing the blood to extend into subcutaneous tissues, results in a bruise having indistinctly appearing edges. Extravasation occurring closer to the surface of the skin results in what is known as an intradermal bruise. A bruise caused by an object having grooves or ridges, such as a ring or a woolen glove covering a fist, can produce a sharply defined, red profile of the object. This type of wound is referred to as a “patterned” injury, and a photograph of the bruise can be compared later to suspected objects.

Bruises caused by cylindrical objects such as pipes and bats produce a pair of parallel, linear bruises caused by the stretching and tearing of blood vessels along edges of the impact area. The bruises are separated by a pale, central area. Such bruises are referred to as tramline bruises. Bruises caused by spherical objects produce circular bruises for the same reason. A group of small round or oval bruises on an arm, a leg, a face or a neck could be the result of someone having been manually restrained, silenced or choked. Defensive bruises on forearms and upper arms indicate attempts to fend off an assailant’s blows.

Bruises are not limited to surface tissues. Bruises can be created within tissues and organs below the skin surface. Periosteal bruises are bone bruises, and they can be severe and quite painful. It is important in forensic autopsies to search for all possible indications of trauma, and that includes bruises beneath the surface of the skin. This might require removing all skin covering a suspected area and special dissection procedures.

The age of bruises, especially if child abuse is involved, can be important. Varying physical factors prevent accurately pinpointing a time of injury; but, due to the degradation of hemoglobin in blood, bruises gradually change color. The sequence of bruise colors reported vary from one report to another but generally runs from red or violet to blue to green to yellow. There is some agreement that a bruise that is green or yellow is at least 18 hours old. A person having bruises of significantly different colors, which suggests that they were inflicted at different times, may well have been a victim of prolonged abuse.

Extra facts

Persons taking blood thinners such as aspirin tend to bruise more readily.

Blood accumulating under the influence of gravity can appear some distance from an actual site of a trauma. Such an appearance behind and below the ear or around the eyes can result from a basilar skull fracture. Bruising around the eyes are known as “racoon eyes” or “panda eyes.”

Robert C. Jones

Viewers of CSI and other crime shows often observe agents comparing fingerprints for possible matches with prints on file in a system referred to as AFIS. DNA is also compared for possible matches with DNA on file in a system known as CODIS. The following includes a brief description of those systems and some other helpful forensic systems and agencies that characters in reader’s future stories might find useful.

According to Webster’s New Collegiate Dictionary, a poison is “a substance that through its chemical action usually kills, injures or impairs an organism” or “a substance that inhibits the activity of another substance or the course of a reaction or process.”

Since there are many types of poisons, only a few of those commonly encountered in novels have room for mention here. For the same reason, acute (relatively quick-acting) poisoning rather than chronic (relatively prolonged) poisoning will be addressed. Many novels and films involved arsenic, cyanide or strychnine. In the film, ARSENIC AND OLD LACE, a pair of spinster aunts murder lonely old men by poisoning them with all three – a glass of home-made elderberry wine laced with arsenic, cyanide and “just a pinch” of strychnine.

Since pathologists now have the ability to detect most poisons, poisoning is no longer the preferred murder method du jour; but there are still enough poisonings to keep pathologists busy. There is no one-test-reveals-all detection system, and pathologists must determine for which poisons they should test. To do this, they evaluate clues that suggest what poison or poisons are involved and how they were administered.

ARSENIC

is a level five (the next to highest, extremely toxic, level) toxin; and it affects the digestive system. Its most common form is arsenic trioxide, a white powder. Other forms include arsenous oxide and arsenic trihydride. Arsenic fumes often have a garlic odor.

Note that a character in your novel who sips a cocktail laced with arsenic should not gasp the words, “You dirty rat,” drop immediately to the floor and neatly expire. Symptoms of arsenic poisoning primarily include severe gastric distress. Other symptoms include esophageal pain, vomiting blood, diarrhea and falling blood pressure. These are often followed by convulsions and coma, and death is usually the final result of circulatory failure.

The symptoms begin after about 30 minutes and death might follow within a few hours but might not occur for some 24 hours. If a victim dies quickly, an autopsy will reveal only an inflamed stomach and perhaps traces of the poison in the digestive tract. Red blood cells will be destroyed, and skin might take on a yellow cast. If death is delayed for several days, arsenic may also be found in the liver and kidneys.

Since arsenic is found in common household items, notably pesticides, it has been a convenient means of murder. Although it is usually swallowed, it can also be inhaled as dust or as arsine gas. Inhalation of arsenic, however, is usually associated with industrial environments. An interesting property of arsenic, although of no concern to victims of acute poisoning, is that it is carcinogenic.

CYANIDE

is a level six (the highest, supertoxic, level) toxin; and it interferes with the absorption of oxygen by the body’s cells. Its most common forms are potassium cyanide, sodium cyanide and hydrogen cyanide. Hydrogen cyanide is also known as prussic acid and hydro cyanic acid. Cyanide involved in television shows is often detected by a bitter almond odor. In reality, it does not always have a detectable odor. Also, some persons are, for genetic reasons, unable to detect the odor. Could these facts be clues in someone’s story? Speaking of clues, note that some burning plastics and fabricated fibers release cyanide gas. Many fires also produce carbon monoxide.

Since cyanide interferes with body-cell absorption of oxygen, it does most harm to the heart and brain, which demand a large amount of oxygen. Although ingesting and absorbing cyanide through the skin can also be toxic, breathing it causes the greatest harm. During WWII, Nazis used hydrogen cyanide in some of their gas chambers. Also, some of our states used it for executions before lethal injections were initiated. Readers might also recall that, in 1973, someone in Chicago laced Extra-Strength Tylenol with cyanide, which killed several persons. Also, in 1978, some 900 cult members at Jonestown, Guyana drank grape-flavored Flavor-Aid laced with cyanide.

In addition to murdering others, cyanide has also been used by many persons to kill themselves. Among the names of those you might recognize are Eva Braun, Delphine Delamare, Hermann, Goering, Heinrich Himmler, Adolph Hitler (cyanide and gunshot), Erwin Rommel and Alan Turing. In addition, of course, are myriad fictional spies who carry cyanide suicide pills to swallow if they are captured. Your cocktail-sipping characters won’t fall immediately to the floor and die after having sampled a cyanide-laced cocktail either, especially if it follows a full meal. A swallowed, lethal dose can produce convulsions, which can be followed by death, but usually only after some four to twelve hours. Sniffing a toxic dose of cyanide in the form of a gas, however, can cause immediate unconsciousness, convulsions and death within fifteen minutes. In fact, hydrogen cyanide, in high concentrations, is known as one of the “one whiff” knockdown gases.

For the files of murder mystery and horror story writers.

Benny was feeling luckier than he had ever felt before as he carefully picked his way through dark woods skirting a long-abandoned logging road. After weeks of effort to gain the trust of a major drug dealer, he was about to meet and make a buy from one of the dealer’s runners. The returns he would get when he distributed the drugs would finance a legitimate business he had been planning to establish for years. Profits to be made in the dope trade could be high, but so could attending risks. Benny was about to learn just how high the risks could be.

He heard a rustle of leaves behind him, but the sound of a gunshot probably had no time to register in his brain as a bullet tore through the back of his skull. A cash-filled briefcase he was carrying hit the ground just before his body did. A gloved hand reached down and retrieved the briefcase. Unhurried feet crunched through dry leaves as they casually made their way toward the road. There was a sound of a car stopping on the road, a door opening and closing and then the fading sound of the car as it drove away. The killing site was quiet. The killer had gone; and, although his body remained, Benny had gone too.

The Sun was just clearing the woods of a thin morning mist when the first insect, a blow fly, arrived at the body. Of the many insects that ultimately appear at such a site, blow flies are usually the first (often within a few minutes of death) and most numerous to arrive and begin colonizing a body. Blow flies have a keen sense of smell and are attracted by odors associated with decay, the odors primarily being the result of actions of bacteria on dead tissues. Blow flies are also the most studied because they usually provide the most accurate information with which to estimate a minimum value for what is known as a post-mortem interval, or PMI. From a minimum PMI, one can estimate a time of death, often referred to on criminal investigation shows as a TOD. Determining a minimum PMI is the primary purpose of forensic entomology. Such information can often be used to narrow a field of murder suspects. The relatively few persons who specialize in studying insects in relation to dead bodies are known as forensic entomologists.

Forensic entomologists are not usually involved in cases that are less than 72 hours old. Prior to that time, other techniques are equal to or more accurate than those involving insects. If a death has occurred more than three days before, however, insects provide the most accurate and often the only method of estimating a minimum PMI. Taking the temperature of a body that has not reached the temperature of its surrounding environment can provide useful information, but its usefulness declines as body temperature drops. Also, since the rate of decreasing body temperature varies from one individual to another, the estimated minimum PMI can vary by as much as two hours.

After about two days, putrefaction begins and body temperature will begin to rise. Chemical reactions of cells in a living body function both aerobically (needing oxygen) and anaerobically (needing no oxygen). Cells that function anaerobically produce lactic acid, which, in a living body, can be reconverted as oxygen is inhaled. In a dead body, of course, this cannot happen; and the lactic acid rises to high levels in muscle cells. Actin and myosin fuse to form a gel, which causes a stiffness known as rigor mortis. It begins about three hours after death, reaches maximum stiffness after about 12 hours, and then gradually dissipates. The latter process is known as resolution of rigor. High environmental temperatures can decrease the reaction time and running or other aerobic exercises before death can produce higher initial levels of lactic acid. In a body submerged in cold water, even after several days, rigor mortis might not begin until the body has been removed from the water. All these factors must be considered when estimating minimum PMI.

During their life time, blowflies pass through four distinct stages. They begin as eggs, of which some 250 might be laid by a fly in body openings such as eyes, noses, mouths and wounds. They then move on to become larvae (maggots), pupae and finally adults. Large numbers of larvae tend to hatch at the same time. They maneuver about a body as a mass, disseminating bacteria and secreting enzymes that enable them to consume nearly all soft tissues of a body.

Time intervals marking the first three of the four stages are relatively predictable, although they vary as a function of factors that include temperature and available food (in the maggot stage). Size and body configuration are the time indicators of maggot stages, known as instars. At a temperature of 70 degrees Fahrenheit (about 22 degrees Celsius), a black blow fly would typically spend 23 hours as an egg, 27 hours as a first instar larva, feeding on the corpse, before molting (shedding its outer layer, or cuticle, to allow growth), 22 hours as a second instar larva before molting, 130 hours as a third instar larva before its outer layer hardens into a puparium, and 143 hours as a pupa before hatching as a fly. The instar stage of a larva can be determined by the number and size of its breathing holes, which are known as spiracles. (Before we take leave of the word spiracles, of interest, but of no particular relevance to the subject, is the method bees use to kill some species of wasps. Rather than stinging them, which often kills the bees themselves, they simply plug their spiracles.)

Surrounding temperatures, and cloud conditions during the periods of insect development must be estimated from records of the nearest weather stations. At warmer temperatures, and with more food available, growth is accelerated. As maggots mass together, their metabolic activity can produce an increase of temperature between 5 and 20 degrees Celsius above that of a surrounding environment. This, of course, represents another variable that must be considered when estimating a minimum PMI.

If there are traces of such toxins as cocaine and heroin in a body, they can increase the growth rate of larvae. If clothing is permeated with such items as oil, paint or fuel, they can slow the colonization rate of insects in a body. Certainly, if a body has been buried, wrapped or refrigerated, that can also slow the growth rate of larvae. Even a lack of insect evidence on a body can be of value. If a body is obviously several days old, and it is summer, the absence can indicate that the body was kept somewhere free of insects until recently.

In addition to the body itself and its clothing, ground beneath it and surrounding it must be examined for insect activity. While in the last instar of majestic maggotry, a full-grown larva eventually stops eating and crawls off, sometimes up to 50 feet, to find a cool, dry place to pupate. It then loosens itself from its outer skin, which hardens (tans) into a hard shell that becomes its puparium. Within the puparium, the now pupa continues to develop until it emerges as an adult. The emerging fly has an interesting system of egress from its puparium. On its head the fly has a sac, known as a ptilinum, that it alternately inflates and deflates to hammer through an end of the puparium.

Other insects also covet dead bodies, each insect having its own cycles to follow. Larvae sometimes have to be reared to adulthood to identify their species. This is important because some insects come at different phases of body decomposition. This is known as insect succession, and it also can provide clues to help estimate minimum PMI. Some insects prefer bodies in sunlight, some in shade, some in open meadows, and some in thickets and dense woods. Different insects are active in different areas in different seasons. All such facts must be considered as potential providers of clues useful in estimating the minimum PMI.

Incidentally, insects can provide useful information concerning more than just PMI. Wounds are sometimes obscured by the effects of decomposition. Since insects usually lay eggs in body openings, activity at a different spot can indicate a possible wound site. In fact insects usually colonize wound sites first. An example is wounds on the palms of hands, which could be indicative of defense wounds.

Since insects also colonize wounds in living persons, they can be used to help estimate when such wounds were inflicted, for example, on an abused child. Maggot presence can also be used to estimate when diapers were last changed on a neglected child or an infirmed adult.

Even if there is insufficient tissue left to determine drug presence, since maggots bioaccumulate, an analysis of their bodies can determine what drugs might have been present in a corpse before death.

If a body has been moved, identifying insects on the body that are native to the original site, where the murder might have occurred, but not to the second, can help locate the original site.

If a killer returns to a murder scene, it often disturbs the insect cycles; and not only might the minimum PMI be determined, but also the date the killer revisited the site.

Insects have also been useful in placing a suspect at a crime scene. A rapist was tied to a rape site using an insect found inside a cocklebur.

As the foregoing attempted to demonstrate, the job of a forensic entomologist involves collecting and evaluating a stupendous amount of information under far less than pleasant conditions.

Two last bits of potentially interesting information: (1) The number of plants pollinated by flies reportedly equals or exceeds the number pollinated by bees (in fact, trees having fruit seeds from which chocolate is ultimately produced are pollinated by flies); and (2) If you open your violin case and find the bow strings ravaged, look for a fly or two. Some flies find horse hair delicious.

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During his seven years on Earth, Devin had not spent much time with his father.  The latter was a heavy drinker and was spending increasing amounts of time away from home.  When his dad was home, he would frequently have intense arguments with Devin’s mother; and many fights were about Devin.  His mother had never wanted him in the first place, and she had often reminded both Devin and his father of that fact.  On Devin’s eighth birthday, his father had left and never returned.

Devin’s mother was overbearing and had made most of the decisions for the household and most for her husband also.  She had always been strict with Devin, and her resentment of him never slackened.  Indeed, it reached new heights when he began to wet his bed, which he continued to do well into his teens.  She rarely struck him, but she frequently abused him verbally by telling him that he was no good, was stupid and would never amount to anything.  She began to date and sometimes brought men home for the night.  Devin would have to stay quietly in his room whenever this happened.

There were no other children nearby with whom he could play when he wasn’t in school, and Devin gradually became a loner.  As such, he never developed socializing skills he would need in adulthood.  He also acquired no capabilities for feeling remorse or empathy.  He effectively lacked a conscience.  As his isolation solidified, his own thoughts and daydreams were all that kept him company.  He had a fertile imagination and was soon getting lost in his own fantasies.  He was to develop an addiction to his fantasies about which his life would turn.  What portion of Devin that remained in the real world would become but a shell.  Fantasies would become his crutch, his coping mechanism for dealing with everyday life; and he would go to extremes to preserve the addiction and, therewith, his coping mechanism.  Addiction is often a mystically comforting presence in the lives of those addicted, and it is a progressive disease.

Devin had long been fascinated by fire, and he used to experiment by burning various materials.  He enjoyed the hypnotic way flames danced and smoke curled.  Somehow, he didn’t feel as lonely or worthless when he was playing with fire.  It had come to represent something akin to a comforting friend.  It wasn’t long before he began to set fire to rubbish and piles of leaves.  Once, his fire spread to a nearby garage.   That brought a fire truck with its siren wailing and neighbors gathering to watch firemen extinguish the blaze.  Devin was the last to leave the scene and frequently returned to view the charred portions of the garage.  It gave him a feeling of power in a strangely sexual way.

After that, his fire-setting regularly included igniting things that belonged to others.  He also began to deface, break and steal things.  Devin had never had a pet but enjoyed playing with neighborhood animals.   His play, however, gradually become rougher and eventually progressed
to outright torment.   While watching the suffering he inflicted on animals, his usual feelings of being inefficacious were replaced by feelings of great power and control … again in a strangely sexual way.

Devin’s isolation and addiction to fantasies grew as did his antisocial behavior.  He killed his first victim with a knife when he was 28.  The victim was tall and had long, dark hair that she wore parted in the middle.  By the time Devin was 34, he had killed seven more woman, all of them tall and having long, dark hair, parted in the middle.  With each killing, Devin had been sharpening his terminating skill to coincide with the perfection of his fantasies but had almost been caught during the last killing.  Devin feared the police might be watching him and that the next killing might be his last, so he wanted it to be perfect.

He selected his victim very carefully.  She lived alone in a small house on a quiet street.  It was Halloween night, and he dressed darkly as appropriate for an executioner.  After the last group of children had received their treats and left the woman’s porch and before the last light in the house had been extinguished, he rang her doorbell.  He stood close to the door and clutched a long knife just inside his open coat.  The woman was apparently expecting to find more children at her door, because she was carrying a basket containing candy when she opened it.  She was tall and had long, dark hair; and it was parted in the middle.  Registering surprise at being confronted by an adult, she took a step backward.  Devin quickly stepped inside.  Closing the door behind him, he said, “Good evening, mother.”

AFTERWORD

The foregoing description is not that of a real person.  There are a number of theories about what factors during childhood lead some to become serial killers.  Some researchers think that the condition is genetic, and some think it is a result of a killer’s environment,  Others think it is the result of both.  What I’ve attempted to offer with Devin’s story is a representative composite of a developing serial killer.  The background of the character described contains a constellation of experiences that are common to many serial killers.  Foremost among them are those known as the MacDonald, or terrible, triad:  These include bed wetting (nearly two-thirds of serial killers wet their beds past the age of 12; fire starting (many serial killers had a fascination with arson or started fires as children; and animal torture (many serial killers progressed to human victims after abusing small or dead animals).  Obsessive daydreams are also common factors.  It is, of course, important to note that few persons having such childhood experiences become serial killers and that daydreams and fantasies that are not obsessive are quite normal; but the daydreams experienced by serial killers are aggressive and develop and expand into their adulthood.  With each victim, they attempt to fine tune their performances so that their real experiences will be as perfect as their fantasies. Serial killer Ted Bundy referred to this as a “learning curve.”  A serial killer learns from the past and is constantly improving.  The emotional stimulation that results seems to induce ever bolder and more frequent attacks, sometimes with a complete disregard of personal risk.  At this stage, there are insufficient internal forces remaining to stop killing.  The only things that can stop the serial killer now are incarceration or death.  Fortunately, most persons who come even from extremely unhealthy backgrounds manage to control antisocial urges that might result from their childhood experiences … but there are always a few who do not.

Many serial killers have an experience known as a precrime stressor as a source of motivation.  In Devin’s case, it was his mother’s rejection.  Killing women like her was his attempt to gain emotional release.   Many serial killers also have particular methods of killing, and they can become the killers’ “trademarks.”

It should also be noted that serial killers rarely harm the major objects of their resentment.  In the foregoing story, Devin killed his mother simply to fulfill the October-horror-story tradition of Storytellers Unplugged writers.  Often, in fact, a serial killer does not even recognize the source of his or her resentment.  For example, David Berkowitz  (aka Son of Sam) reportedly stated that he had nothing against women and that he had no idea why he killed them.  Like Devin, however, he had been unwanted by his mother; and most of the women he killed resembled her.

Psychology is not an exact science, and attempts to categorize persons with psychological problems have led to categories that are not perfectly consistent.  Medical and legal definitions differ, and the latter even differ from state to state.

The following is an attempt to provide writers with information that is generally representative of a majority of serial killers.  To begin, let’s differentiate between types of multiple murderers – those who have killed at least two other persons.  As typically defined, major types include the following:

Mass murderers are those who kill at least four victims at one location during one continuous period.  The period can extend from the time it takes to fire a gun four times to a number of days.  The victims can be persons who live or work together or who simply happen to be at the same location.

Spree killers are those who kill at least two persons, each at a different location.  The killings are grouped as a single event because there is not what the FBI refers to as a “cooling off” period between murders.

Serial killers are those who kill at least three persons, each on separate occasions.  They usually plan ahead to murder selected victims, and they have cooling-off periods between killings.  Some kill victims in one area and others kill in distantly spaced locations.  Serial killers can be placed in two categories:  psychotics and psychopaths.  The former are legally insane and cannot differentiate between right and wrong.  Psychopaths are in touch with reality and can differentiate between right and wrong and appear to be normal, but they lack much of a conscience.  Psychopaths arguably have the most deviant minds that exist and should be the most feared.

Additionally, there is a subgroup of serial killers:

Visionary killers are commonly psychotic and murder certain persons because “voices” order them to do so.  Only about 10 percent of serial killers are psychotic, however.  David Berkowitz is an example of a psychotic.

Mission-oriented killers try to fulfill a “mission” to rid society of certain groups of persons, for example, prostitutes, that they consider as being too unworthy to live.

Hedonistic killers murder because they enjoy the pleasure it gives them.

The most common type of serial killer is out for power and control over their victims.  These often engage in rituals that mimic abuse they themselves suffered.

There is commonly a sexually related motive involved in male serial killings, and they are typically violent.  Most merge sex and violence into a single fantasy.  Male serial killers usually kill for elusive psychological gains.  They more often kill strangers, torture or mutilate, and report a sexual motive.  Money is a far more common motive for female serial killers, and the manner in which women kill is usually not very violent.  Poisoning is a fairly commonly used method; and their victims are usually husbands, persons in hospitals or nursing homes and relatively defenseless children and elderly persons.  Note, however, that it is not at all rare for females with antisocial personality disorder (APD) to manipulate a male to kill for her. That fact might produce an interesting plot twist.  Heterosexual male serial killers usually kill women and children; homosexual male serial killers usually kill gay men, prostitutes and hitchhikers.

Studies show that potential serial killers became solidified in their loneliness between the ages of 8 and 12, and such isolation is considered by some experts to be the single most important aspect of their psychological makeup.  Isolation, though, does not mean that all potential killers are destined to be introverted and shy.  Many are extroverted and conversationally adept, which belies their inner isolation.  Many believe that all serial killers are insane or are driven by voices only they can hear and/or hallucinations that only they can see.  These are categorized as visionaries, and they are relatively rare (only about ten percent of serial killers are psychotic), but voices reportedly told Herbert Mullins to kill to prevent earthquakes in California.  During his trial, he took pains to point out that, during his 13-victim murder spree, California was indeed spared from earthquakes.

Fantasy cannot be overemphasized as being an extremely important factor in the development of a serial killer.  Some have daydreams about domination and murder even prior to their adolescence.  Often, elements of their fantasies carry over into their subsequent real crimes.

The following are some serial-killer-related statistics (some of which vary from source to source):

Most are in 20s or 30s when first they kill
Less than 20 % kill for money
22% kill at least one stranger
58% set fires, destroy property and steal
62% kill strangers exclusively
67% are rebellious  and have nightmares
68% are bed wetters
71% kill in a specific location or area
71% have isolated childhoods and lie habitually
80% run away from home
83% have severe temper tantrums
85% are Caucasian
88% are male

Note that the foregoing statistics are generally shared by serial killers but should not be assumed to apply rigorously to a specific individual.

Now that you all have the foregoing to keep you awake at night, I must add that serial killings are not necessarily the work of lone killers.  One can share his killings with another person while still being addicted to the same fantasy.  In fact, killings have been recorded that were done not only by pairs but by dysfunctional families.

As you might imagine, there is a huge amount of information about serial killers in the form of accounts and theories – much too much to include in a simple essay – so I have mercifully limited these remarks to a piece that will take readers less than a whole afternoon to read.

Have a  haunting Halloween, everyone; but be careful for whom you open your door.  THEY are out there . . . somewhere.

RCJ

R. C. Jones

The buzzing sound began as I started down a narrow set of stairs leading to a large basement room. I had never been there before, but I knew what the source of the buzzing must be. It was the sound of a small vibrating saw cutting off the top of someone’s skull.

READER ALERT! Anyone with an especially queasy stomach might wish to abandon ship here.

In my last essay, we got as far as what happens forensically to bullets, cartridge casings and primers when cartridges are fired in revolvers and semi-automatic pistols. But what happens forensically to bodies of victims who do not survive being caught in front of those weapons when they are fired? The following gives some details about that. The details are described as I observed them on a visit to a county morgue to observe autopsies performed on two such victims. Trainees at a local police academy were required to attend a post-mortem examination (autopsy), and a trainee-friend invited me to accompany him and four others.

For reader convenience, insider jargon and certain key terms are presented in uppercase letters.

A forensic autopsy, as contrasted with a clinical or academic autopsy, is performed when a death might be related to a crime. The word “autopsy” refers to a post-mortem examination performed on a human; “necropsy” refers to one performed on a nonhuman.

There was an expected chemical odor present in the basement room, but it was relatively mild – - what I would call a force-1 odor. There were no seriously decomposing bodies to be examined that morning so we were fortunately spared any full, force-10 odors. We six observers took up station in a small, slightly elevated, viewing area disposed at one end of the room. The room housed a number of autopsy tables. The tables were formed of stainless steel and were tilted a bit so that water and body fluids would run toward drains at their lower ends. Each table had raised edges to prevent fluids from running onto the floor. Above each table hung lights, a weight scale, a microphone for recording notes and a water hose for rinsing away fluids.

Upon the first table lay the body of a 28-year-old man who had been shot during a fight in a pool hall. A small, dissecting table was mounted above the body’s legs. A block had been placed under the head so that the scalp faced upwardly. A pathologist had made an incision that began behind one ear, passed across the top of the scalp, and ended behind the opposite ear. He had then pulled the front portion of the scalp over the face and the rear portion over the back of the neck to expose the top of the skull. Next, he had used the vibrating saw, which is usually referred to as a STRYKER SAW (no matter which manufacturer produced it), to cut through the skull. The saw had a semicircular, toothed blade that oscillated back and forth rapidly over an angular displacement of only about 20 degrees. It thus cut through bone but not soft tissue. If you have ever had a plaster cast cut off, you have
probably seen such a saw in action.

After having cut and removed the upper skull portion, called a calvarium, the pathologist extracted a .32 caliber bullet from the brain with forceps, usually referred to as PICK-UPS. He rinsed the bullet with water and dropped it into a small metal tray with a clink just like that heard in many CSI episodes. (Those readers who have seen the brain transplant scene in Robocop 2 would also have recognized the sucking-grating sounds created when the calvarium was removed.) The brain was then cut loose from the spinal cord and other attachments with a scalpel, weighed and suspended by a string in a jar filled with FORMALIN, which is a buffered-water solution of formaldehyde. A brain is very soft, and suspending it prevents it from becoming flattened as a result of resting upon the bottom of the jar. The formalin preserves the brain and, after a few weeks, also makes it sufficiently firm to resist falling apart during an examination.

The pathologist recorded descriptions of any abnormalities on exterior surfaces of the body and positioned a BODY BLOCK under the back of the body. The block forced the chest upwardly in preparation for an examination of interior organs. Using a large scalpel, the pathologist made a Y-shaped incision. Upper portions of the Y extended from each shoulder to the lower end of the sternum (breast bone). From that
point, the lower portion of the Y extended to the pubic bone. The lower incision detoured a bit around the umbilicus (navel). If the body had been that of a woman, the upper incisions would have detoured around and below the breasts.

Using a scalpel, the pathologist separated the skin and muscle from the chest wall and pulled the resulting flap up over the body’s face to expose the rib cage. The odor at this point had elevated to force-2, which was still relatively mild. If you can recall the odor of raw lamb meat, you are now as good as being in the autopsy room.

The pathologist used a large, curved bone cutter to snip ribs along each side of the rib cage. This, with the aid of a scalpel, separated the chest plate (the sternum and ribs connected to it) from the remainder of the skeleton and exposed the lungs and heart, the latter still being enclosed within a pericardial sac. Slicing the abdominal muscle away from the diaphragm and the bottom of the rib cage exposed the abdominal organs. The pathologist severed all the connections of remaining internal organs to the body with a scalpel and placed them on the dissecting table. Using a scalpel, scissors, forceps and a very long knife commonly referred to as a BREAD KNIFE, he separated the organs. He simply pulled several items apart, a technique referred to as BLUNT DISSECTION. He separated the lungs, weighed them and sliced them with the bread knife into bread-slice-thick portions. He removed and weighed the heart, opened it and examined it, and systematically removed, weighed and examined remaining organs and glands.

Although the man on the table had been only 28 years of age, he had been a heavy smoker and a heavy drinker. Both his lungs and his liver were already black. Two of the observers were smokers, and both mumbled something at this point about never smoking again. One of them later lit up before he even reached his car.

The pathologist took samples from many of the organs and placed them in plastic cassettes. The samples were later to be fixed, waxed, sliced into sections five microns thick, mounted on glass slides, stained, coverslipped and examined using a microscope. The slides must be kept at least twenty years and are often kept indefinitely. Additional small samples are preserved in formalin, in what is referred to as a SAVE JAR, at least until a final report has been prepared, and are later incinerated.

As one can imagine, as the autopsy had progressed, the odor intensity had been creeping ever higher. By this time, it resided at about a force-5 level. When the pathologist opened the stomach, an unforgettable odor of gastric (hydrochloric) acid drove it up to a force-7 level. When he opened the intestines over a sink to flush the contents down the drain with water, a procedure referred to as RUNNING THE GUT, we were assaulted by force-9 fragrances normally associated with diarrhea and vomit.

At this point, the pathologist replaced the calvarium upon the lower skull and sewed the separated scalp together using a baseball stitch. The incision would be covered by a pillow in a casket. He then put the organs, glands and such removed from the body in a transparent plastic bag. He placed the bag within the empty body, balanced the chest plate atop the bag, and sewed the Y-shaped incision together, again using a baseball stitch. After rinsing the body using the water hose and a sponge, he covered it with a sheet. A mortician would later pick up the body, inject embalming fluid into the carotid and subclavian arteries in the neck and upper chest and the femoral arteries in the thighs, insert filler into the chest cavity to restore an approximately faithful exterior configuration to the body, apply makeup and otherwise prepare the body for public viewing.

After an appropriate fixing time, the brain would have been examined in much the same manner as were the organs and glands. Sections would have been removed for microscopic examination, a few portions put into a save jar, and the rest incinerated.

A subsequent autopsy was performed on a young policeman who had lost a desperate struggle with a motorist he had just stopped. The policeman had been shot in the right side of his chest with his own gun, a .38 caliber revolver. The bullet had punctured his aorta. The autopsy proceeded in the same order as the first except that removing his brain was left until last. I add this description to include an additional detail.

Four of our initial group of six observers had left by this time, but I had stayed to ask the pathologist some questions. One was about how he could estimate the path of a bullet inside a body. He invited me to stand across the table from him so that he could show me one of the tricks of his trade. He first showed me the entry wound from the outside and pointed out a darkened area of skin around one edge of it. He explained that the area was a burn produced by the rapidly spinning bullet as it had pierced the skin. When a bullet passes through skin along a path that is at right angles to the body surface, it leaves a fairly symmetric-appearing hole. If the path is not at right angles, skin along the side of the entry hole at which the angle of the bullet relative to the skin surface is less than 90 degrees will often be scorched by thermal energy resulting from friction between the spinning bullet and the skin. Don’t bother rereading the previous sentence, just imagine inserting a pencil through such a hole and inclining it toward the darkened edge. The inclined pencil will point in the general direction taken by the bullet.

The chest plate had been removed from the body, and the pathologist had pushed aside some of the intestines to give me an inside view of the hole made by the penetrating bullet. From the shape and location of the scorched, outside area, he had estimated where the bullet had probably stopped and found it within a few seconds. Of interest but of no particular relevance was the fact that the pathologist also discovered and showed me that the policeman had three spleens, an anomaly he said was not particularly rare.

I had been a bit concerned about what my reaction might be to watching a human body being cut open, but the only thing that bothered me was the force-9 odors. As the pathologist pushed intestines away from the bullet hole, the slippery conduits kept oozing between and around his fingers to refill the cavity he had just excavated so that he had to keep repeating his actions to maintain a clear view. Fortunately, I remained absorbed only in what he was explaining.

During a radio call-in show, a doctor had responded to a question about how he had overcome revulsion when confronted by the sight of the inside of a human body. He said that, just as he had always thought that the exterior of a body was beautiful, he found the inside to be beautiful also. When I considered the functional complexity of a body’s parts, I felt much the same way. In a college biology class, we students had to dissect a Necturus maculosus (mudpuppy, or waterdog). It was interesting, and I had no revulsion problems with it; but, for weeks thereafter, whenever I looked at anyone, I could not help visualizing their insides. I thought I might again experience this interesting phenomenon after watching the autopsies, but I did not.

* * * * *

For the sake of brevity, I have referred to a single pathologist as being the one who performed the autopsies described. Often, there are a number of persons, having specific titles (e.g., dieners and prosectors), who perform different functions during an autopsy.

* * * * *

I should have mentioned one more detail. A pathologist also checks a toe tag to ensure he has the correct body. Ideally, he does this before making very many incisions.

Robert C. Jones

R C Jones

In case some of you unpluggers might someday wish to write about a situation involving a shooting, some information about firearm identification might come in handy. First, a bit of basic background. For the sake of brevity, I will limit the discussion to handguns, that is, to revolvers and semi-automatic pistols. Both fire cartridges each of which comprises a casing, within which is held an explosive powder, a bullet held in the forward end of the casing, and a primer disposed at the base, or head, of the casing.

Each type of handgun has at least one chamber within which a cartridge is fired when a spring-driven hammer is released by a trigger and slams a firing pin against the primer. When struck, the primer ignites the powder; and rapidly expanding gases from the burning powder accelerate the bullet through a barrel. Helically shaped riflings within the barrel spin a passing bullet, giving it an improved trajectory.

A major difference between the two types of handguns is that a revolver has a cylinder in which there are usually five or six chambers, and a pistol has but one chamber located at the rear end of its barrel. The cylinder in a revolver serves as a storage area for cartridges and is rotatable so that each chamber can be brought to a position behind and in line with the barrel. One cartridge can be stored in the chamber of a pistol, and others are stored in a magazine, or clip. After a revolver is fired, rotating the cylinder brings a successive cartridge into alignment with the barrel.
Revolvers come in two basic flavors: single action and double action. In a single-action revolver, the hammer is cocked to rotate the cylinder; and a trigger is then pulled to release the hammer and fire a cartridge. In a double-action revolver, pulling the trigger cocks the hammer, rotates the cylinder and releases the hammer to fire a cartridge. In a semi-automatic pistol, when a cartridge is fired, recoil forces are used to recock the hammer, to cause an extractor to yank the empty casing from the chamber and to cause an ejector to expel the casing from the gun. Spring forces are then used to inject a fresh cartridge into the chamber.

Most of us have probably seen movies where crime-scene evidence is analyzed by experts. Among the items popularly eyeballed are, of course, recovered bullets. These are often shown clamped in a pair of optically bridged macroscopes and rotated to compare striations carved into one bullet by barrel rifling with striations carved into another bullet. A crime-scene bullet and sample bullets fired by a suspect gun can be so compared to link the former bullet to the suspect gun. Fired bullets retrieved from different crime sites can be compared to link separate shootings to each other.

I have heard TV and movie experts mention fingerprints left on a gun or cartridges, powder residue, the caliber of bullets and striated marks carved by rifling. They have even mentioned whether the rifling had a right-handed or left-handed twist. I missed it, however, if they ever mentioned the rifling twist rate – the number of inches of rifled barrel needed to twist a bullet completely around once.

In addition to rifling striations, which reflect imperfections in rifling associated with a particular gun, the caliber, weight and shape of a bullet are all clues that help limit the number of guns that could have been involved in a shooting to those made by a certain manufacturer during a certain period. In fact, there are many more things to consider than one might think.

Recovered cartridge casings, colloquially referred to as brass even though they are made from a number of different metals, can be a repository of many additional clues. A chamber itself can have rough portions that scratch a cartridge casing as the casing is loaded and unloaded, even if the cartridge is not fired. Since casings expand within a chamber when fired, they are then even more susceptible to being scratched while being unloaded.

After a firing pin strikes a cartridge primer, the pin might remain slightly imbedded in the primer. If the pistol is one where a barrel drops slightly when a recoil forces an action open, the firing pin might be dragged across the primer as the pin is retracted from the impression, leaving what is known as a firing pin drag mark. As a fired cartridge recoils, its base and primer are forced against a breech face having a hole through which the firing pin struck the primer. A portion of the primer might be forced into the hole. If the barrel drops, the primer can be scratched by an edge of the hole to create what is known as a shear mark. When a recoiling cartridge is forced against a breech face, any imperfections in the face will be imbedded in the primer. Such marks are known as breech marks.

A casing of most cartridges has a circular extractor groove near its base. As previously mentioned, recoil forces cause an extractor to hook into the extractor groove and extract an empty casing from a chamber; and an ejector ejects the casing from the gun. The action of the extractor can leave extractor marks, and that of the ejector, ejector marks, even if the cartridge is not fired. Ejector marks can be in the form of both striations and impressions.

A firing pin, in addition to leaving drag marks, also leaves impressions in primers. The impression size, shape, depth, surface imperfections and strike position are all clues to compare with cartridges fired by a suspect gun. They can also be helpful in determining the type and make of the gun that fired them.

One thing I would like to know is why, on law enforcement shows, do they handle evidence with rubber gloves as if that would not smear any existing fingerprints.

— R. C. Jones