CHAPTER 5

TIME OF
DEATH:

A CRITICAL PART OF THE TIMELINE

Just about every murder mystery you read or watch on television has a question about the time of death. The same is true for news stories about real-life murders. Why do the police spend so much time on making this determination? Why is the time of death argued about in court, each side trying to tweak the timeline to its advantage? Because the time of death can exonerate a suspect or focus suspicion on him. It can substantiate or refute witness and suspect statements. It can literally make or break the case. It is one of the most important functions of the ME.

Before we look at why this estimation is so important, let’s first understand what we mean by the term time of death.

DEFINING TIME OF DEATH

There are several times of death. Let me repeat that: There are several times of death. Time of death seems to be a simple and straightforward term that obviously means the exact time that the victim drew his last breath. Unfortunately, it’s not quite that simple. There are actually three different times of death: the physiologic time of death, when the victim’s vital functions actually ceased; he legal time of death, the time recorded on the death certificate; the estimated time of death, the time the ME estimates that death occurred.

It is important to note that the estimated time of death can vary greatly from the legal time of death and the physiological time of death.

The only absolutely accurate determination of the time of death is the uncommon circumstance in which a person died with a physician or other skilled medical professional present. The doctor could make the determination and mark the time, and even this is assuming his watch or the clock on the wall was accurate. But that little inaccuracy aside, a death witnessed in this fashion is the only time that the three above times of death would correlate with one another.

Otherwise, it is impossible to determine the exact time of death. But what if someone witnessed the fatal blow or gunshot or what if the event was recorded on a timed surveillance camera; wouldn’t that accurately mark the time of death? The answer is a qualified yes. If the witnessed event led to immediate death, the witness would have seen the actual death. If not, the witnessed event is simply the trauma that led to death but not the actual moment of death. People can survive massive and apparently lethal injuries for hours and even days or years.

But most deaths are not witnessed. Natural death may come during sleep, and accidental and suicidal deaths often occur when the victim is alone. In homicides, the perpetrator is typically the only witness and he rarely checks his watch, and even if he did, he’s not likely to talk about it. This means that when the ME must determine the time of death he can only estimate the approximate time.

These times of death may differ by days, weeks, or even months if the body is not found until well after physiological death has occurred. For example, if a serial killer killed a victim in July, but the body was not discovered until October, the physiologic death took place in July, but the legal death is marked as October, since that is when the corpse was discovered and the death was legally noted. The ME estimated that the time of death could be July, or it could be June or August. It is only an estimate and many factors can conspire to confuse this determination. But, it is critically important for the ME to be as accurate as possible.

THE IMPORTANCE OF THE TIME OF DEATH

An accurate estimation of the time of death can lead to discovering the identity of the assailant. In criminal cases, it can eliminate some suspects while focusing attention on others. For example, a husband says that he left for a business meeting at 2 P.M. and returned at 8 P.M. to find his wife dead. He says that he was home all morning and that she was alive and well when he left. If the ME determines the time of death was between 10 A.M. and noon, the husband has a great deal of explaining to do. On the other hand, if the estimation reveals that the death occurred between 4 and 6 P.M., and the husband has a reliable alibi for that time period, the investigation will move in a different direction.

Notice that in the above example the ME gave a range rather than an exact time for his estimated time of death. He didn’t say 4:30 P.M. but rather said between 4 and 6 P.M. Simply put, that’s the best he can do and that’s why it’s called the estimated time of death. It’s a best guess.

The time of death is not confined to criminal investigations; it can also come into play in civil situations. Insurance payments may depend upon whether the insured individual was alive at the time the policy went into effect or if he died before the policy expired. Even a single day can be important. Likewise, property inheritance can hinge on when the deceased actually died. Suppose two business partners die near the same time. Their contract may read that the company assets go to the survivor if one of them dies. In this case, the heirs of the one who died last would own the company assets. Similarly, the dispersal of property under a will might be affected by which partner died first.

DETERMINATION OF THE TIME OF DEATH

Determining the time of death is both an art and a science and requires that the ME use several techniques and observations to make his estimate. As a general rule, the sooner after death the body is examined, the more accurate this estimate will be.

Unfortunately, the changes that a body undergoes after death occur in widely variable ways and with unpredictable time frames. There is no single factor that will accurately indicate the time of physiological death. It is always a best guess. But when the principles are properly applied, the ME can often estimate the physiological time of death with some degree of accuracy.

To help with his estimation, the ME utilizes various observations and tests, including:

• body temperature

• rigor mortis

• livor mortis (lividity)

• degree of putrefaction

• stomach contents

• corneal cloudiness

• vitreous potassium level

• insect activity

• scene markers

The most important and most commonly used of these are body temperature, rigor mortis, and lividity. French physician Dr. Alexandre Lacassagne (1843– 1924), director of Legal Medicine in Lyon, France, wrote extensively on algor mortis (the temperature of death), rigor mortis (the stiffness of death), and livor mortis (the color of death).

BODY TEMPERATURE

Normal body temperature is 98.6ºF After death, the body loses or gains heat progressively until it equilibrates with that of the surrounding medium. Since corpse temperature can be easily and quickly obtained (we’ll look at how shortly), the search for a formula that uses this parameter to define the time of death has been sought for years. As early as 1839, English physician John Davey undertook the study of corpse heat loss in London, and as late as 1962, T.K. Marshall and F.E. Hoare attempted to standardize this analysis when they established a computerized mathematical formula known as the Standard Cooling Curve. In the intervening years, and even since Marshall and Hoare, many others have attempted to devise similar schemes. Unfortunately, none of these have proven to be any more accurate than the current formula for heat loss of 1.5 degrees per hour.

The formula is:

Hours since death = 98.6 - corpse core temperature / 1.5

This approximate rate of heat loss continues until the environmental temperature is attained, after which it remains stable. That sounds simple enough.

Unfortunately, it’s not quite that straightforward. The 1.5-degrees-per-hour factor varies, depending upon the environment surrounding the body, the size of the corpse, clothing, and other factors. For example, a body in a temperate room will lose heat much more slowly than will one in an icy, flowing stream. And a body in a hot environment, such as an enclosed garage in Phoenix, Arizona, in August, where the ambient temperature could be 125ºF or more, will gain heat. The key is that the corpse will lose or gain heat until it reaches equilibrium with its environment.

The coroner’s technician who processes the corpse at the scene takes a body temperature, and also measures the temperature of the surrounding medium—air, water, snow, or soil (if the body is buried). Ideally, the body temperature is taken either rectally or by measuring the liver temperature, which may be a more accurate reflection of the true core body temperature. This requires making a small incision in the upper right abdomen and passing the thermometer into the tissue of the liver. This should only be done by a trained individual and under the direction of the ME. Care should be taken not to alter or destroy any existing wounds on the body. Some people have suggested measuring the core temperature by inserting the thermometer into a knife wound or gunshot injury to negate the need to make a new incision. This should never be done because the introduction of any foreign object may contaminate or alter the wound, which can be key evidence in the case. For practical reasons, the rectal temperature is usually taken.

The sooner after death the body is found, the more accurately the time of death can be assessed by this method. Once the body reaches ambient temperature, all bets are off. But even if done correctly and soon after death, body temperature determination is subject to several sources of inaccuracy.

One assumption made in the calculations is the initial body temperature. The normal 98.6ºF is an average and varies from person to person. Some people have higher normal temperatures than others. Women tend to run higher temperatures than do men. Illnesses associated with fevers can markedly elevate the temperature of the person at the time of death, while chronic illness, dehydration, or the presence of prolonged shock may lower initial body temperature. There is also some diurnal (basically, morning versus evening) variation in body temperature in most people. All this means that the calculation begins with some degree of error.

A dead body loses heat passively by three distinct mechanisms: radiation (heat lost as infrared heat rays), conduction (heat passed on to any object that contacts the body), and convection (heat lost into the moving air). The state of the corpse and the environmental conditions greatly affect the rate of heat loss.

Obesity, heavy clothing, warm still air, exposure to direct sunlight, and an enclosed environment slow heat loss. Fat and clothing make good insulators, so an obese person in a sweater will lose heat much more slowly than would a thin, unclothed corpse exposed to cold or moving air, water, or shade. Children and the elderly tend to lose heat faster, as do those who are chronically ill or emaciated. If the body is in contact with cold surfaces such as marble or cool concrete, heat loss will be greater.

There’s still one more curveball: Several days after death, as fly maggots begin to feed on the corpse, their activity and internal metabolic processes can at times raise the temperature of the corpse. This should not be a problem for the forensic investigator, though, because once this insect activity is that far advanced body temperature is no longer of use.

As you can see, heat loss is fraught with inaccuracies. Still, with early and careful measurement of the core body temperature and consideration for the conditions surrounding the corpse, a reasonably accurate estimate can be made.

Let’s say two people are murdered in a home in Houston, Texas, during late summer. The bodies are discovered four hours after death. One body is left in the garage where the ambient temperature is 110ºF, while the other is in the living room where air conditioning holds the temperature at 72. The corpse inside would lose heat at about 1.5 degrees per hour, so that if the ME had evidence that the death had occurred four hours earlier, he would expect to find a core body temperature of approximately 92ºF to 93ºF.

1.5 degrees / hour x 4 hours = 6 degrees

98.6 – 6 = 92.6

If he found a different core temperature, he would revise his estimate. But what if the victim were very old or young, thin, unclothed, or lying on a cold tile floor near an air conditioning vent? Under these circumstances, the heat loss would be more rapid. The core temperature could be 88ºF to 90ºF, perhaps even less. If the ME failed to consider these mitigating factors, an erroneous estimate of the time of death could result. For example, if the core temperature was 88ºF and he failed to adjust for the environmental conditions around the body, he could estimate that approximately seven hours had elapsed since death.

98.6 – 88 = 10.6 / 1.5 = 7.1 hours

An estimate of six to eight hours is quite different from an estimate of three to five hours. The killer may have an ironclad alibi for the former time period, and easily could since he hadn’t arrived at the crime scene at that time. He could have been having lunch with twenty people. But only four hours later, he might not have such an alibi.

What of the body in the garage? The ME would expect the corpse to gain heat at the same rate of 1.5 degrees per hour. Thus, the core temperature should be approximately 104ºF, or perhaps even higher.

RIGOR MORTIS

Rigor mortis is the stiffening and contraction of the muscles due to chemical reactions that take place within the muscle cells after death. The chemical reaction that causes this is the loss of adenosine triphosphate (ATP) from the muscles. ATP serves as energy for muscular activity. Without it, our muscles could not contract. The presence and stability of ATP depends on a steady supply of oxygen and nutrients, which are lost with the cessation of cardiac activity that occurs at death. When the ATP levels fall, the muscles contract and stiffen, producing the rigidity of rigor. The later loss of this rigidity and the appearance of flaccidity (relaxation) of the muscles occur when the muscle tissue itself begins to decompose as part of the putrefaction process.

It is important to note that rigor begins throughout the body at the same time but the appearance of the actual rigidity doesn’t. It typically follows a predictable pattern, being detectable first in the small muscles of the face, neck, and hands before progressing to the larger muscles. The reason for this progression from smaller to larger muscles is simply that smaller muscles possess less ATP so the loss is relatively more rapid, and smaller muscles will exhibit stiffening more readily than will larger ones.

The rigor begins in about two hours and the entire contracting process takes about twelve hours. At that time, the body is completely stiff and is fixed in the position of death; it tends to remain so for another twelve hours. This is called the rigid stage of rigor mortis. The process then reverses itself with rigidity being lost in the same fashion, beginning with the small muscles and progressing to the larger ones. This process requires another twelve or so hours. The muscles are now flaccid (relaxed); this is termed the flaccid stage of rigor mortis.

A good general rule for rigor mortis is 12-12-12: it maximizes at twelve hours, remains unchanged for twelve hours, and resolves over the next twelve hours. So, rigor is only useful in the first thirty-six hours or so after death. Under normal conditions, that is. There are wide variations from corpse to corpse and from situation to situation. These variations make rigor one of the least reliable methods of determining the time of death. To understand these variations, let’s look at the physiology behind this process.

Sometimes rigor mortis comes on very quickly after death. This occurs in any situation that leads to a premortem (before death) depletion of ATP. If the muscles are already very low on ATP at the time of death, the contraction and stiffening of the muscles will occur more rapidly.

Muscular activity and excessive body heat are the two most important conditions that lead to ATP depletion. Any severe muscular activity around the time of death quickens the onset of rigor. For example, the victim could have been running, fighting with an assailant, struggling to prevent drowning, or suffering from violent seizures. Each of these would consume most, if not all, of the muscular ATP and rigor could come on within minutes of death. Interestingly, a victim who was chased prior to death may show the first signs of rigor in the legs, where the ATP would be most depleted in this circumstance. Strychnine is a drug that causes convulsions and muscular spasms, conditions that mimic severe physical activity. Victims of strychnine poisoning may develop rigor almost immediately.

Since an elevated body temperature also causes increased ATP consumption, any drugs or infectious processes that increased the body temperature could cause a rapid onset of rigor. Victims of sepsis (infection throughout the bloodstream), pneumonia, or any other febrile (fever) process, as well as those that succumb to heat stroke, may develop rigor very rapidly.

The opposite is also true. Cold conditions slow the process of ATP loss considerably and will delay the onset and development of rigor. A victim who dies from exposure in a cold clime or one that is frozen immediately after death may not develop rigor for days, perhaps not until the body is warmed or thawed.

In addition, for reasons that are not well understood, obese people tend to develop rigor at a slower pace than do thin individuals. In fact, obese persons sometimes don’t develop rigor at all.

Rigor can be broken by bending and stretching the corpse, which breaks up the muscle fibers. Once broken, rigor will not return.

Cadaveric spasm is the instantaneous onset of stiffness throughout the body, which locks the corpse in the exact posture it was in at the moment of death. The corpse could be frozen sitting, kneeling, reaching, or in virtually any position. Cadaveric spasm occurs under extremely violent physical and emotional situations. A victim may be holding a knife at the moment of death and cadaveric spasm will cause the hand to get a death grip on the weapon.

Though somewhat controversial, cadaveric spasm is best viewed as simply instantaneous rigor. This makes sense since the conditions that cause cadaveric spasm are similar to those that cause early onset of rigor.

LIVOR MORTIS

Corpses typically contain a dark discoloration of portions of the body. This discoloration is livor mortis (also called lividity or post-mortem hypostasis). It is important for two reasons: It can help determine the time of death and, as important if not more so, can indicate whether a body was moved after death.

Lividity is a purplish hue of the tissues and may be mistaken for bruising by the inexperienced. It is caused by stagnation of blood in the vessels. At death, the heart stops beating and the blood ceases to move. Gravity then causes the stagnant blood to settle into the dependent (lower) areas of the body. This means that a supine corpse (lying with the face upward) will develop lividity along the back and buttocks. A corpse lying on its left side will show lividity along the downside of the left shoulder, arm, hip, and leg.

However, any dependent area that presses against a firm surface will appear pale and will be surrounded by the lividity. For example, a corpse lying on its back will show lividity along its entire lower surface except where the body actually contacts the hard floor. The back of the head, shoulder blades, buttocks, and calves will show pale points of contact, because the weight of the body compresses the blood vessels in these support areas and prevents the accumulation of stagnant blood. Tight clothing may do the same thing. A belt, waistband, or brassiere may leave a pale track through an area of lividity.

Why is the lividity this dusky color? Blood that is rich in oxygen (O₂) is bright red, whereas blood that is depleted of oxygen is purple. At death, when the heart and circulation cease, no fresh blood reaches the cells of the body. In a futile attempt to survive, the cells of the body extract all the oxygen they can, leaving the blood depleted of it. This oxygen-poor blood is dark purple, and when it settles it produces purple lividity.

But, not all lividity is bluish or purplish in color. In carbon monoxide (CO) and cyanide (CN) poisoning (see Chapter Eleven), the lividity may take on a cherry-red or pinkish coloration. Carbon monoxide combines with hemoglobin creating carboxyhemoglobin, which is bright red in color. Similarly, cyanide combines with hemoglobin to produce cyanohemoglobin, also bright red in color. In addition, cyanide is a “metabolic” poison that prevents the body’s cells from using oxygen. Since the cells no longer take in oxygen, the blood remains rich in oxygen, which also gives it a bright red color. So blood that is rich in carboxyhemoglobin, cyanohemoglobin, or oxygen is bright red and the resulting lividity reflects this.

Another common situation that may produce red lividity is when the victim is exposed to very cold conditions near and after the time of death. In this case, the cold slows down all cellular activities, including the post-mortem removal of oxygen from the blood, which leaves the blood rich in oxygen and red in color so any lividity will be red or pink.

In individuals who exsanguinate (bleed to death), there may be little or no lividity, since there is little blood remaining that can settle. Typically, the entire body will be pale. Alternatively, people dying from severe heart failure, shock, or asphyxia may develop deeply purple lividity. The blood in these situations is usually poorly oxygenated during life and is thus deeply purple in color, which means any lividity will be also.

Lividity typically appears between thirty minutes and two hours after death and reaches its maximum by eight to twelve hours. Initially, this discoloration can be shifted by rolling the body to a different position. If a body is supine for a couple of hours and then rolled to its left side, the lividity that had begun accumulating along the back will shift and begin accumulating along the left side. But, by six to eight hours, the lividity becomes fixed. This means that rolling the body to another position will not result in a shifting of the discoloration. The reason is that after about six to eight hours, the blood vessels in the area begin to break down, and the blood seeps from the vessels and stains the surrounding tissues. As opposed to the blood that remains within the vascular system, this blood in the tissue is fixed in position. The ME can use shifting and fixed lividity to estimate time of death and to determine if the body has been moved or repositioned, something the dead do not do without assistance.

If a body is found face-down with fixed lividity along the chest, abdomen, and front of the legs, the ME can conclude that the death was at least six to eight hours earlier. It may be longer but it is not likely sooner. If the lividity can still be shifted, death likely occurred less than four hours or so earlier. On the other hand, if a body is found face-down, but with fixed lividity along the back, then the body was moved at least six hours after death, but not earlier or the lividity would have shifted to the newly dependent area. This means the body lay on its back for at least six hours after death, long enough for the lividity to become fixed, and was then rolled to its stomach or moved to an entirely different location and deposited on its stomach.

This fixing process is not an all-or-nothing phenomenon. It occurs gradually. This means that by four to six hours some of the lividity might be fixed and some still able to shift. If the ME finds that the corpse has some faint areas of fixed lividity along the back and true fixed lividity along the front, he might conclude that the body laid on its back for around four hours and was then moved and placed face-down, where it laid for six or so hours more.

This same process occurs in the internal organs. At the autopsy of a person found supine, the ME would expect to find a settling of the blood along the posterior (back) areas of the lungs, liver, spleen, brain, and other internal organs. This may present a problem because a victim left in the supine position accumulates blood along the back of his scalp and the back of his brain. Blood may even seep into the subdural space (between the brain and the skull). At first examination, this may appear similar to someone who was struck in the back of the head with a blunt object, contusing (bruising) the scalp and brain. The ME must make the distinction by using his knowledge and experience.

From this you can see that the careful examination of the lividity pattern of a corpse can provide critical evidence in homicide cases. It can help reconstruct the sequence of events surrounding the death. If the patterns and the body position don’t match, it suggests that someone had reason to move the body. That someone is most likely, but not always, the killer. Sometimes a family member who finds a loved one dead will want to clean up or reposition the body to a more acceptable position or place before calling the police.

All these mental gymnastics presume normal circumstances. Since body decay depends primarily on the ambient temperature, and since the fixing of the lividity is due to breakdown of the blood vessels and the seepage of the released blood into the tissues, anything that hastens or slows the decay process will do the same for the fixation of lividity. In hot and humid environments this fixation may occur in as little as three or four hours, while in colder climes, it may take as long as thirty-six hours.

THE RATE OF BODY DECAY

Putrefaction is the term used for decay or decomposition of a body. Under normal circumstances it follows a predictable pattern, which the ME can use in his estimation of the time of death.

At death, all vital processes within the body stop. The heart doesn’t beat, the blood doesn’t flow, and all body processes cease. For many years it was believed that the hair and nails continued to grow for a while after death. This was actually stated as fact by Charles Meymott Tidy in his book Legal Medicine (1882). The reason for this erroneous belief is that as fluids are lost from the corpse, the tissues retract or shrink so that it appears as if the nails and hair are longer several days after death than they were at the time of death.

The decomposition of the human body begins immediately after death and involves two distinct processes: autolysis and putrefaction. Autolysis is basically a process of self-digestion. After death, the enzymes within the body’s cells begin the chemical breakdown of the cells and tissues. As with most chemical reactions, the process is hastened by heat and slowed by cold. Putrefaction is the bacteria-mediated destruction of the body’s tissues. The responsible bacteria mostly come from the intestinal tract of the deceased, though environmental bacteria and yeasts contribute in many situations. Bacteria thrive in warm, moist environments and become sluggish in colder climes. Freezing will stop their activities completely. A frozen body will not undergo putrefaction until it thaws.

Putrefaction is an ugly and unpleasant process, which under normal temperate conditions follows a known sequence. During the first twenty-four hours, the abdomen takes on a greenish discoloration, which spreads to the neck, shoulders, and head. Bloating, caused by the accumulation of gas within the body’s cavities and skin as a byproduct of the action of bacteria, soon follows. This begins in the face where the features swell and the eyes and tongue protrude. The skin will then begin to marble, and a web-like pattern of blood vessels forms over the face, chest, abdomen, and extremities. This marbling is green-black in color and is due to the reaction of the blood’s hemoglobin with hydrogen sulfide. As gases continue to accumulate, the abdomen swells and the skin begins to blister. Soon, skin and hair slippage occur and the fingernails begin to slough off. By this stage, the body has taken on a greenish-black color. The fluids of decomposition, or purge fluid, begin to drain from the nose and mouth. This may look like bleeding from trauma, but is due to extensive breakdown of the body’s tissues.

However, the rate at which this process occurs is almost never normal because conditions surrounding the body are almost never normal. Both environmental and internal body conditions alter this process greatly. Obesity, excess clothing, and a hot and humid environment speed this process, while a thin, unclothed corpse lying on a cold surface with a cool breeze follows a much slower decomposition process. Very cold climes may slow the process so much that, even after several months, the body appears as if it has been dead only a day or two. Freezing will protect the body from putrefaction if the body is frozen before the process begins. Once putrefaction sets in, even freezing the body may not prevent its eventual decay. If frozen quickly enough, the body may be preserved for years.

Sepsis (blood infection) is particularly destructive to the body and might accelerate the decay process so much that, after only twenty-four hours, the corpse could appear as if five or six days had passed. The reason is that not only would the body temperature be higher at death in this circumstance, but also the septic process would have spread bacteria throughout the body. This allows the decay process to begin quickly and in a widespread fashion.

The internal organs tend to decay in a predictable order. The ME can use this in his estimation of time of death. The stomach and intestines, which hold many bacterial species, decay first, followed by the liver, lungs, and brain, and then the kidneys. Lastly, the uterus and prostate succumb to the bacteria.

Left unchecked, the decomposition process will ultimately leave behind only a skeleton. The time required for a body to completely skeletonize is determined by the environmental conditions we’ve been discussing. And the process is not always uniform. Occasionally, the decomposition is spotty so that portions of a body decay while others are left more or less intact.

Another important factor in the rate of decay is the location of the body. A body exposed to the environment will decay faster than will one that is buried or in water. The general rule is that one week exposed above ground equals two weeks in water and eight weeks in the ground. Also, bodies left exposed or in shallow graves are subject to predators.

Dead bodies attract dogs, cats, bears, hogs, rats, and other predators. They might feed on the flesh and carry away portions of the corpse. The remaining flesh and bones may reveal claw and tooth marks that might reveal the predatory species. For example, dogs and cats tend to remove V-shaped wedges of tissue, while rodents tend to leave shallower, smooth-edged wounds. Rodent incisors (front teeth) leave parallel grooves on the surface of gnawed bones. The ME looks for evidence of predator activity since their activities may bear on his estimated time of death.

But decomposition is not the only way a body can change after death. Under certain circumstances mummification or adipocere formation may occur.

Mummification occurs when the body desiccates (dries out) in a hot, dry environment. The low humidity inhibits bacterial growth and putrefaction, while at the same time sucking the moisture from the tissues. In ancient Egypt, spices and salts were rubbed on the corpse to hasten the drying process so that the corpse would mummify rather than decay. A leathery, dark-colored corpse results. Its appearance is as if the flesh had been “shrink-wrapped” over the bones. This is a similar process to the making of beef jerky. The internal organs may dry and shrivel or become a dark brownish-black putty-like material. Mummified corpses tend to remain intact for long periods of time.

Adipocere is the result of a chemical process called saponification, which is basically soap making. Adipocere is caused by a reaction between certain bacteria and the body’s adipose (fatty) tissues. Bacteria such as Clostridium perfringens, the bacterium that causes gas gangrene, convert body fat into oleic, stearic, and palmitic acids, the primary constitutes of adipocere. The result is a brownish gray, greasy or waxy substance, which can cast the body into a statue-like form. On first glance, the corpse may appear as a mannequin, or as if it had been carved from a large bar of soap. Adipocere most often occurs in bodies found in water or warm, damp areas and usually takes several months to form so it is a broad indicator of time of death. A corpse that has significant adipocere formation could not have been dead only a couple of weeks.

Bodies may not decompose uniformly. A corpse may be partially skeletonized, partially mummified, and partially converted to adipocere. Incomplete embalming may lead to partial preservation and partial skeletonization.

One other decomposition state worth covering is the bloated condition of floaters, bodies of people who either die in water or are dumped into water shortly after death. Initially the body sinks, but as putrefaction occurs and gases accumulate in the body’s tissues and cavities, the body rises to the surface and floats. Since the production of these gases is a byproduct of the action of bacteria, it is greatly affected by the temperature of the water. In the warm waters of the Gulf of Mexico, where the warmth accelerates bacterial growth and gas formation, a body may float after only a week or two, while in cold waters, where bacteria multiply more sluggishly, it may take weeks or months.

In general, bodies found in temperate water display:

• swollen hands and face after two to three days

• separation of skin from the body after five to six days

• loss of fingernails after eight to ten days

• floating after fourteen or so days in warm water and after three or four weeks in cooler water

The appearance of each of these physical signs is extremely variable and depends on many conditions within the corpse and in the water.

TIME SINCE DEATH

One of the most difficult tasks for the ME is determining the approximate time of death in a corpse that is weeks or months old. In this situation, body temperature, rigor mortis, and lividity are no longer useful, so the ME will use the expected stages of post-mortem decay and then modify that timeline according to the local conditions where the body is found.

The average temperature and humidity are key to his assessment. A corpse dumped in a cool mountain cave decays much more slowly than one left lying in a sunny field. A buried corpse decomposes at a slower rate than one that is exposed to the open air. Bacterial growth tends to be less vigorous in a buried corpse, and predators and climate changes are less likely to damage the body. Shallow graves, less than two or three feet deep, suffer some temperature variations that parallel the environmental temperature changes, while those buried more deeply are exposed to relatively stable temperatures.

The ME might consult with a forensic climatologist to see what the recent daily high and nightly low temperatures have been and use this information to refine his time estimate. For example, a corpse left in a wooded area in the Colorado mountains decomposes much faster if the average daily high and low was 85ºF and 65ºF, respectively, as compared to 65ºF and 45ºF. A corpse exposed to a heat wave for four or five days might look like one exposed to more normal temperatures for ten to fourteen days.

In buried corpses, the moisture in the soil affects the rapidity of decay, with more moisture translating to more rapid decay. The amount of moisture in the soil at a burial site depends on the relative humidity, the amount of rainfall, and the degree to which the soil drains. Graves in moist, rainy, and low-lying areas would contain more water than those on a hillside in a drier area. The ME must consider these variables in his estimation.

To further complicate things, the body’s location and degree of exposure might change at any point after death. Murder victims may be stored for a few days prior to burial or dumping and are sometimes moved from one site to another. The killer simply might not have had enough time to get rid of the body at the time of the murder and might return later after he has developed a plan for disposal. Or the corpse might be moved because the police are getting too close to locating it, or as part of a serial killer’s sick fantasy. The body might even be moved by nonhuman agents, such as water or landslides.

The passage of several days between the death and the burial of the victim presents the ME with changing exposure conditions that can introduce errors into his time of death estimation. He looks for evidence that the body has been moved and attempts to analyze each place where the body lay, estimating how long it lay there in order to make an educated guess of time of death. This is quite difficult, and often impossible.

Consider a body dumped in a lake that is then retrieved two days later and buried. Or one that is weighted down and dumped in a cold river, then breaks free from its bonds and washes downstream, and finally comes to rest on an isolated sunny shore where it is found four days later. Or a body that is buried for a week, and then dug up and moved to another burial site with entirely different soil and water conditions. Or a body in a cave that is dragged into the sunlight by predators. In each of these situations, the corpse is exposed to varying environmental conditions for varying amounts of time.

THE LAST MEAL

The ME can often use the contents of the victim’s stomach to help determine time of death. After a meal, the stomach empties in approximately two hours, depending on the type and amount of food ingested. If a victim’s 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 four hours after eating. Additionally, if the small intestine is also empty, death probably occurred some twelve hours or more after the last meal.

If the medical examiner can find out through witness statements when the last meal was consumed, he can use this to determine the time of death. Let’s say a man is found dead in a hotel room and the ME determines that his stomach is full of undigested food materials. If he had dinner with a business associate from 8 to 10 P.M., then returned to his room, the finding of a full stomach would indicate that the death occurred shortly after he returned to his room. The ME might place the time of death between 10 P.M. and midnight.

These calculations depend on a number of factors. Heavy meals and those rich in protein and fat digest more slowly than do small meals and those high in carbohydrates, sugars, and liquids. The consumption of alcohol or many sedative and narcotic drugs, as well as some medical conditions, tend to slow digestion and gastric emptying, while other drugs and medical conditions hasten these processes. Also, there is great individual variation in rate of digestion. Therefore, gastric contents are of marginal help in time of death determinations.

THE EYES

The clear covering over eye pupils are called corneas. At death they become cloudy and opaque. This may occur in a very few hours if the eyes are open at death, or it may take up to twenty-four hours if they are closed.

The vitreous humor is the clear, thick, liquid substance that fills the eyeballs. After death, the concentration of potassium within the vitreous increases at a constant rate over the first few days. This increase is due to release of potassium from red blood cells into the vitreous. Though the determination of the vitreous potassium level is only useful in the first three or four days, as opposed to many other post-mortem changes, it is independent of ambient temperature.

INSECTS

Besides animal predators, a dead body attracts numerous insects. These are typically flies and beetles that feed off the corpse’s flesh. They tend to appear at predictable times and in a predictable sequence, which the ME will use to aid in his determination of the time of death. Unfortunately, these patterns vary greatly by geographic region, specific locale, time of day, and season. Because of the complex nature of the bug world, the ME will often request the assistance of a forensic entomologist. Entomology is the study of insects and forensic entomology is the study of the insects that populate a dead body.

The first use of insects to solve a crime dates back to thirteenth-century China. In the first forensic text in 1235, Sung Tz’u described the case of a murder using a sickle. The villagers were forced to line up and lay their sickles on the ground before them. Flies congregated around one attracted by the remnants of the victim’s blood on the blade. Thinking this must be some divine finger pointing at him, the killer confessed. Modern forensic entomology began in France in the mid-1800s, culminating with the publications of two forensic entomological texts by Jean Pierre Mégnin (1828–1905): Faune des Tombeaux (Fauna of the Tombs) in 1887 and La faune des cadavres application de l’entomologie à la médecine légale (The Fauna of Cadavers in Forensic Entomology) in 1894. The American Board of Forensic Entomology was founded in 1996.

During the first seventy-two hours after death, the ME employs all of the non-entomological methods for determining the time of death and makes his best guess. After that time, entomology is the most accurate method of making this determination.

Insects help to determine the time of death in two basic ways: The first method uses the predictable developmental stages of insects, most notably the blowfly; the second addresses the predictable succession of insect species that populate the corpse.

Numerous species either feed on the dead body, on the insects that are attracted to the body, or both. Each has a preferred time and order of appearance and a different life cycle. It is well beyond the scope of this text to consider this subject in any great detail, so let’s confine ourselves to the most common species, the blowfly. An understanding of this insect will give you a feel for the problems the forensic entomologist faces.

When a body is left exposed, blowflies appear early, often within the first hour after death. They seek out the moist areas of the corpse, such as the nose, mouth, armpit, groin, and open wounds, to lay their eggs. The eggs hatch to larvae (maggots) within hours. Over the next ten days, the larvae feed, grow, and repeatedly molt. There are tables that show the growth rate of these larvae so that the entomologist can compare those found at the scene with the tables of length, and therefore estimate the age of the larvae. Using this method he can usually say whether the larvae are three days old or nine days old. After the larval stage, the maturing flies become pupae, which is when their outer covering hardens. Approximately twelve days later adult flies emerge. So, this entire cycle takes from about eighteen to twenty-two days. The mature flies will then lay eggs and the cycle repeats.

Under normal circumstances, if the ME or the entomologist finds only eggs, the death likely occurred less than forty-eight hours earlier. If he finds maggots but no pupae, the death occurred between two and ten days earlier. The finding of pupae indicates that ten or more days have passed, while the presence of mature hatchlings indicate that death occurred two to three weeks earlier.

As you might suspect, it’s not really that easy. Blowflies do not deposit eggs at night, and they are less plentiful and even absent in winter. So, if the victim was murdered at midnight, the blowflies may not appear until dawn, and if it is cold out, they may not appear at all. In unfavorable conditions, the maggots may go dormant for extended periods of time. If the body is in an area that is warm during the day and very cold at night, they may be dormant half of each twenty-four-hour period. Also, if it turns cold for several days, the developmental process may be put on hold for that time period. The entomologist might consult a forensic climatologist, who can provide information regarding the temperature and weather conditions over the past days and weeks.

Fly activity is typically delayed in a corpse enclosed in a structure. It may not occur at all if the corpse is in a container, such as a car trunk or barrel or plastic sheeting. While a buried corpse may not attract flies, other insects do attack the corpse. Each of these situations must be considered when insect activity is used to determine the time of death.

Most of the time, insect studies can only give a minimum time since death occurred. If pupae are found, the corpse must be at least six to ten days old. It can’t be less since the pupae would not have had time to appear, but if the weather is inhospitable to the larvae, it could be much longer. Another compounding factor is that the insects appear in waves and new generations appear all the time. The adults produced after two weeks will themselves lay eggs and these eggs will follow a similar cycle. So a three-week-old corpse may show fly eggs, maggots, pupae, and adults. Sorting all this out is no easy task.

Insects might also show that the corpse has been moved. A corpse found to be populated with insects that are not found in the area of its discovery suggests that the corpse had at one time been where these species of insects live, and therefore, must have been moved.

Another use of insects is in the field of toxicology (see Chapter Eleven). Insects feeding on the tissues of the corpse ingest whatever chemicals are contained within the tissues. If a corpse is too decayed for adequate toxicological testing, the insect larvae might reveal the presence of a toxin. Some chemicals retard the maturation rate of the larvae, while others accelerate it; this might alter the estimation of time of death.

Live maggots, pupae, and empty pupal cases, are collected as samples for the entomologist to evaluate the types of insects present and where each is within its developmental cycle, and estimate how many cycles have occurred. Some maggots should be placed in a KAAD solution (a mixture of alcohol, kerosene, and other chemicals) or alcohol. This will preserve them in a state that reflects the scene.

SCENE MARKERS

The ME uses everything at his disposal to estimate the time of death, including many non-scientific findings. Scene markers include any information at the scene or from witnesses or family and friends. The last time the person was seen alive serves as a starting point. The individual must have died at some time after the sighting—if that sighting is accurate. Family and friends can speak to the person’s habits and any changes they have observed.

Missed appointments or work, missed daily walks or visits to the coffee shop, uncollected mail or newspapers, and dated sales receipts can be useful. In assaults, a broken watch or clock may give the exact time of the event. The absence of home lights or the lack of smoke from a chimney might strike the neighbors as odd.

The victim’s clothing might be helpful. For example, if the victim has missed work for two days and is found near the front door of his home, dressed in work attire and carrying his car keys, it is logical to assume that he was headed to work at the time of his death. Or perhaps he had a racquetball game scheduled but never showed. He is then found in his garage, wearing his exercise gear. In this case, he likely died as he was leaving for his game.

Let’s say a neighbor knows that the person goes for a walk every morning at 7 A.M., but has not done so for two days. Lights are on in the house but no one answers the door, so the police are called. They enter to find a corpse sitting in a chair, facing the television that is on and tuned to a certain channel. Next to his chair is a TV Guide, opened to the listings for three days earlier and a show on the very channel the television is tuned to is circled. This evidence suggests that the victim died three days earlier around the time of the show in question. Or not. It’s a best guess situation and the ME would add this information to the more scientific determinations discussed earlier before making a final estimate. But these scene markers can help him narrow the time.

PUTTING IT ALL TOGETHER

As you can see, determining the time of death is not an easy matter. No single test or observation will give an exact time, so the ME uses all available testing and puts it together in an attempt to arrive at some reasonable range for the time of physiological death.

Let’s say a body is found at 6 A.M. The on-scene analysis reveals that the body temperature is 90ºF, lividity is fixed, rigor is full, and no appreciable insect activity is noted. How would the ME use this to determine the time of death? The body temperature suggests that death occurred six or so hours earlier, and the lividity would give a range of six to eight hours. Typically, full rigor would take eight to twelve hours to occur. The lack of insect activity is expected since the death took place after sunset. Since none of these are absolute times, the ME combines them for a best guess. He might conclude the most likely range would be six to nine hours and place the time of death between 9 P.M. and midnight the previous day. That’s the best he could do, but it might be enough if the prime suspect has no alibi for that time period.

THE BODY FARM

No discussion of the time of death would be complete without mention of the Body Farm (officially the University of Tennessee Forensic Anthropology Facility) and its contribution to the field of taphonomy (see Chapter Four: Identifying the Body, “Time Since Death”).

In 1971, Dr. William M. Bass, a forensic anthropologist, established the Body Farm at the University of Tennessee in Knoxville as a place where he could study the rate and pattern of decomposition of bodies under various environmental conditions. He basically created an outdoor taphonomy laboratory.

Bass began with a single body, but now has studied hundreds. At any one time, the three-acre farm may have as many as 150 bodies decomposing in the open in either sun or shade, buried at various depths and in varying soil conditions, in water, in the trunks of cars, stuffed in trash bags, rolled in carpeting, interred beneath concrete slabs, or hanging from scaffolding. With each body, our understanding of the decay process increases. In fact, virtually everything we know about corpse decomposition came from Bass’s farm.

The FBI regularly uses Bass’s expertise and the information obtained from the research at the Body Farm. They even send agents there for training. In the future, the Body Farm wants to produce an atlas of body decomposition for law enforcement and help perfect ground-penetrating radar and other body-locating techniques, including an “electronic nose” for sniffing out corpses. The main goal is to understand the chemistry of decomposition better so that more accurate estimations of the time of death become possible.