There are many things that, when misinterpreted, can result in inaccurate crime scene investigation results. The following describe some potential misinterpretations.
Body positions:
Bodies burned in a fire often assume a pose commonly referred to as a “pugilist position.” Their hands are clenched and raised like those of a prize fighter. This could be misinterpreted to mean that the victim was fighting or trying to ward off an attacker when killed. Actually, the pose is simply the result of the heat of the fire causing muscles to contract.
Bullet and knife wounds:
When bullets or knives penetrate skin, the skin stretches a bit as it is being pierced. Consequently, bullet and knife wounds often appear to be smaller than the objects that caused them. This applies to bullet entry wounds but not to bullet exit wounds. Depending on the type of bullet and its path inside a body, it can be deformed or even split into several pieces. As a result, exit wounds can be of many shapes and sizes.
Lividity:
The term “lividity” refers to blood that, due to death, ceases to flow under the urging of a beating heart and settles under the urging of gravity into the lowest parts of a body. These parts assume a reddish-purple color. An exception would be a bright red color when death is the result of carbon monoxide poisoning. Another exception would be when low areas are under great pressure. This can cause light marks to appear within the overall lividity coloration. An inexperienced investigator might confuse the marks with bruising.
Interestingly, if a body has been in one position, say, on its back on a floor for some time, lividity will form in the lower parts. If the body is then moved, say, into a chair, the lividity does not reposition itself. This, of course, indicates the body was not originally positioned in the chair and can indicate how the body was originally positioned.
Lividity is not an accurate indicator of time of death. It usually begins to appear between twenty minutes and four hours after death and completes within twelve hours.
Rigor mortis:
Rigor mortis (roughly Latin for stiffness of death) refers to a chemical process that takes place in muscles after death and results in a stiffening of joints – so stiff that it can take considerable force (sometimes applied by several persons) to change the positions of a corpse’s limbs. A common misconception is that a medical examiner can accurately determine a time of death as a function of the stiffness of a corpse, but its onset and completion are functions of a number of variable factors. An extreme example is that of an emaciated baby that suffered crib death and was found to be in a complete state of rigor mortis within two hours of death. Rigor mortis usually, however, begins between two and six hours and completes between two and six additional hours. It begins in strong persons faster than in an average person and lasts longer. In a weak person, it begins later and lasts for a much shorter time. It both begins and ends faster for bodies in hot locations. In extremely cold locations, it begins faster and lasts for a much longer time. Stiffness in a body found in a very cold location can easily be mistaken as being the result of rigor mortis or freezing or vice versa. Rigor mortis typically begins in the face muscles and then proceeds in general order to the jaw, upper extremities, trunk and lower extremities. Some muscles relax before rigor mortis sets in, however. The jaw usually drops open, and the eyelids remain open.
Cadaveric spasm:
Sometimes referred to as instant rigor mortis, and sometimes mistaken for actual rigor mortis, a cadaveric spasm is a seizing of muscles that can occur when the moment of death occurs during extreme exertion by skeletal muscles. Such might occur, for example, when a person is shot in the head while struggling with an attacker. Other examples might be when a person drowns while trying to swim to safety or has a heart attack while running a marathon. Cadaveric spasm can lock a body in such positions as sitting or kneeling with arms outstretched. Hands are often clenched and can enclose hair, fabric or other evidence torn from an attacker.
Algor mortis:
Often thought to refer to the relaxation of rigor mortis, algor mortis (roughly Latin for coolness of death) actually refers to the cooling phase undergone by a corpse after death. In cases where a person has undergone prolonged torture just before death, body temperature might actually rise for an hour following death before dropping. Being a function of a number of variable factors, the temperature of a body is also not a very accurate indication of time of death. Variable factors include the initial temperature of the body, the ambient temperature at the location, the weight and condition of the body, the humidity and the air movement. These factors are then applied to a formula. An estimate is that temperature drops at a rate of 0.8 degrees Kelvin per hour. Some estimates set it at a two-degree drop during the first hour and a one-degree drop per hour thereafter.
Postmortem movement:
Body movements usually cease within seconds or minutes after death but, at least temporarily, may be taken as signs of life. The movements can include those within a range extending between fingers twitching and, as in one case, a portion (the myocardium) of a heart continuing to beat until rigor mortis was well underway.
Strangulation:
First of all, choking and strangulation are not the same. Choking refers to asphyxia caused by an internal blockage of the airway and is usually accidental. Strangulation refers to asphyxia caused by an externally applied pressure that closes airways and blood vessels in the neck and is usually intentional. Ten percent of all violent deaths are the result of strangulation. Strangulation cuts off oxygen to the brain, and this leads to death in about four minutes. Persons deprived of oxygen for some 10 seconds lose consciousness, and those deprived for 50 seconds rarely recover. If both arteries leading to the brain are closed by strangulation, death can result in less than 12 seconds. In crime videos, investigators often report a body’s broken hyoid bone as if it and strangulation always went together. Broken hyoid bones, however, reportedly occur in only 10 percent of strangulation cases. A San Diego study of 300 strangulation cases revealed that half had no visible signs of strangulation. Even petechiae (small red or purple spots caused by underlying broken capillaries) are not always present after a strangulation. Other signs that are often visible include red eye hemorrhages, bruising, scratching, tongue swelling, urination, defecation and even miscarriage.
Decomposition:
Decomposition is included here simply to note that, because it shares some of the signs of strangulation, care must be taken to prevent determining an incorrect cause of death.
Extra facts:
Many are under the impression that, when a TV character playing a lawyer mentions the words “corpus delicti,” s/he is referring to the lack of a dead body. Actually, the words refer to a body of evidence. A human body is not required to obtain a murder conviction.
On the subject of body temperature, a mistake is sometimes made by an inexperienced investigator by placing a thermometer in a body’s mouth. After death, this does not reveal the core temperature of a body. Such a measurement must be taken at the other end of the body.
On the subject of motion after death, chickens flutter for a time after having their heads removed in anticipation of a Thanksgiving dinner. In his book, PRESCRIPTION – MEDICIDE: THE GOODNESS OF PLANNED DEATH, Jack Kevorkian reportedly described how a few sadistic officers in the Shah of Iran’s army would bet on how far condemned men could run after being beheaded as they started to run. These phenomena indicate that postmortem motion might be related to directions from the brain just before death.
