D. P. Lyle, M. D.
The timing of death is both an art and a science.
Unless the death is witnessed, it is impossible to determine the exact time of death. The Medical Examiner (ME) can only “estimate” the approximate time of demise. It is important to note that this “estimated time of death” can vary greatly from the “legal” time of death, which is the time recorded on the death certificate, or the “physiologic” time of death, which is when vital functions actually cease. The “legal” time of death is the time the body was discovered or the time a doctor or other qualified person pronounced the victim dead.
These “times of death” may differ by days, weeks, even months, if the body is not found until well after “physiologic” death has occurred. For example, if a serial killer kills a victim in July, but the body is not discovered until October, the “physiologic” death took place in July, but the “legal” death is marked as October. The ME’s “estimated time of death” would be July.
That said, the ME can estimate the “physiologic” time of death with some degree of accuracy. He uses the decompositional changes that occur in the human body after death to help him in this endeavor. These changes consist of measuring the drop in body temperature, the degree of rigidity (rigor mortis), the degree of discoloration (livor mortis or lividity), the stage of body decomposition, stomach contents, and other factors. Bodies found in water present special problems in this regard.
Normal body temperature during life is 98.6 degrees F. After death, the body loses heat progressively until it equilibrates with that of the surrounding medium. The rate of this heat loss is approximately 1.5 degrees per hour until the environmental temperature is attained, then it remains stable. Obviously, this measure is greatly effected by location. A body in the snow in Minnesota in January and one in a Louisiana swamp in August will lose heat a widely divergent rates. These factors must be considered in any “estimate” of time of death.
The criminalist who processes the scene should take a body temperature and measure the temperature of the surrounding medium--air, water, snow, earth (if the body is buried). Ideally, the body temperature is taken rectally. Obviously, the sooner after death the body is found, the more accurately time of death can be assessed by this method. Once the body reaches ambient temperature, all bets are off.
Rigor mortis is the the stiffening and contraction of the muscles due to chemical reactions that take place in the muscle cells after death.
It typically follows a predictable pattern. Rigidity begins in the small muscles of the face and neck and progresses downward in a “head-to-toe” fashion to the larger muscles. The entire process takes about 8-12 hours. At that time, the body is completely stiff and is “fixed” in the position of death. Then, the process reverses itself, with rigidity being lost in the same fashion, beginning with the small muscles and progressing to the larger ones. This process begins 18 to 36 hours after death and is usually complete within 48 hours. So, rigor is only useful in the first 48 to 60 hours after death.
The reason for the rigidity, is the loss of adenosine triphosphate, or ATP, from the muscles. ATP is the compound that serves as energy for muscular activity and it’s presence and stability depend upon a steady supply of oxygen and nutrients, which are lost with the cessation of cardiac activity. The later loss of rigidity and the appearance of flaccidity (relaxation) of the muscles, occurs when the muscle tissue itself begins to decompose.
Rigor is one of the least reliable methods for determining time of death because it is extremely variable. Heat quickens the process, while cold slows it. Obese people may not develop rigor, while in thin victims it tends to occur rapidly. If the victim struggled before death and consumed much of his muscular ATP, the process is hastened.
Lividity is caused by stagnation of blood in the vessels. It lends a purplish color to the tissues. The blood, following the dictates of gravity, seeps into the dependent parts of the body--along the back and buttocks of a victim who is supine after death. Initially, this discoloration can be “shifted” by rolling the body to a different position, but by 6 to 8 hours, it becomes “fixed.” If a body is found face down, but with fixed lividity along the back, then the body was moved at least 6 hours after death, but not earlier or the lividity would have “shifted” to the newly dependent area.
At death, the body begins to decompose. Bacteria go to work on the tissues and by 24 to 36 hours the smell of rotting flesh appears and the skin takes on a progressive greenish-red color. By 3 days, gas forms in the body cavities and beneath the skin, which may leak fluid and split. From there, things get worse. Add to this, predation by animals and insects and the body can become completely skeletonized before long. In hot, humid climes, this can happen in 3 or 4 weeks.
The ME can often use the contents of the victims stomach to help determine time of death. After a meal, the stomach empties itself in approximately 4 to 6 hours, depending on the type and amount of food ingested. If a victim stomach contains largely undigested food material, then the death likely occurred within an hour or two of the meal. If the stomach is empty, the death likely occurred more than six hours after eating. Additionally, if the small intestine is also empty, death probably occurred some 12 hours or more after the last meal.
“Floaters” are corpses found floating in a body of water. They present special problems for the ME in determining the time of death. Water temperature of course has an effect as do local tides and predators. The general rule regarding decomposition is that one week on dry land equals two weeks for a submerged body.
To become a “floater,” a body must to be in the water long enough for tissue decomposition from bacteria to begin. This process forms gas as a byproduct, which collects beneath the skin and in body cavities. Bodies tend to sink, then rise again in several days when the gas forms, adding buoyancy. They thus become "floaters."
Under these circumstances, the hands and feet swell (several days), the outer layer of skin separates from the underlying tissues (5-6 days), the skin of the hands and the nails separate (8-10 days), and entire body swells shortly thereafter. Tissues become extremely fragile and are easily damaged during removal from the water.
Timing of the “floating” depends upon several factors, including water temperature, currents, the size of the victim, and other variables. For example, a body will “float” after 8-10 days in warm water and 2-3 weeks if in colder water. Cold slows the process of decomposition.
As you can see, the timing of a victim’s death is a very inexact science and is greatly altered by the environment. In cold areas, body temperature changes are magnified, but decomposition changes are slowed, The inverse is true for hot, humid climes. Add to this, predation by insects and animals and the ME’s job can become difficult.