Measuring body temperature

Normal living body temperature in most people is 98.6 degrees Fahrenheit (37 degrees Celsius). After death, the body loses heat at a rate of about 1.5 degrees per hour until it reaches ambient temperature (the temperature of its environment). This rate varies, however, depending upon the environment surrounding the body: A body in a warm room loses heat much slower than one in an icy, flowing stream.

The criminalist who processes the scene takes a body temperature and measures the temperature of the surrounding air, water, snow, or soil (if the body is buried). Ideally, body temperature is taken rectally. Another method is taking a liver temperature, which may be a more accurate reflection of the true core body temperature.

The sooner after death that 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.

Obesity; clothing; warm, still air; exposure to direct sunlight; and an enclosed environment slow heat loss. Fat and clothing make good insulators. A thin, unclothed corpse exposed to cold or moving air or water, or one deposited in an area shaded from direct sunlight, loses heat faster. Children and the elderly tend to lose heat more rapidly, as do people who are chronically ill or emaciated. Whenever the body is in contact with cold surfaces such as marble or cool concrete, heat loss is greater.

As with all methods for determining the time of death, heat loss is fraught with inaccuracies. Nevertheless, with early and careful measurement of the core body temperature and with consideration for the conditions surrounding the body, the ME can make a reasonably accurate estimate.

Stiffening up: Rigor mortis

You’ve probably heard the term stiff used in reference to a corpse. I can almost hear Bogart mumbling it right now: “Who’s the stiff?” Although the term may not be kind, it is accurate. It refers to rigor mortis, or the stiffening and contraction of muscles caused by chemical reactions that take place in the muscle cells after death.

The reason the body becomes rigid after death is the loss of adenosine triphosphate (ATP) from the muscles. ATP is the compound that serves as energy for muscular activity. Through a chemical reaction that converts ATP to adenosine diphosphate (ADP), energy is produced and this energy causes the muscle to contract. The presence and stability of ATP depends on a steady supply of oxygen and nutrients, which are lost when the heart stops. In turn, the ATP then converts to ADP and the muscles stiffen, producing the rigidity of rigor mortis. The later loss of rigidity and appearance of flaccidity of the muscles occur when the muscle tissue itself begins to decompose as part of the putrefaction process.

Rigor mortis begins throughout the body at the same time, but the muscles become rigid at different rates in a predictable pattern. When conditions are normal (ambient temperature is about 70 degrees Fahrenheit), rigor mortis sets in as follows:

• Beginning about two hours after death, rigor mortis is first detectable in the small muscles of the face and neck and progresses downward in a head-to-toe fashion to the larger muscles.
• The entire contracting process takes about 8 to 12 hours, after which the body is completely stiff and is fixed in the position of death.
• The body remains fixed for another 12 to 18 hours, a state that is called the rigid stage of rigor mortis.
• The process reverses itself, and rigidity is lost in the order in which it appeared, beginning with the small muscles and progressing to the larger ones.
• After another 12 hours or so, the muscles become relaxed in the flaccid stage of rigor mortis.

The general rule is 12-12-12. Rigor comes on over 12 hours, remains for 12 hours, and then resolves over 12 hours. More or less, anyway.

Because of this process, rigor mortis is useful only for estimating time of death during the first 36 to 48 hours after death — under normal conditions, that is.

Sometimes rigor mortis comes on very quickly after death, especially when ATP levels have been reduced before death, usually by intense physical activity or body heat, both of which can rapidly deplete ATP levels. Examples include the following:

• A victim who ran from an assailant prior to death may show the first signs of rigor in the legs, which is where the ATP would be most depleted.
• Victims of strychnine poisoning may develop rigor almost immediately because strychnine causes convulsions and muscular spasms that mimic intense physical activity.
• Because an elevated body temperature also causes increased ATP consumption, victims of sepsis (infection throughout the bloodstream), pneumonia, or any other febrile (fever-causing) process, or those who succumb to heat stroke may rapidly develop rigor mortis.

Cold conditions, on the other hand, slow the process of ATP loss considerably and delay the onset and development of rigor. A victim who dies from exposure in a cold climate or one who is frozen immediately after death may not develop rigor for days, perhaps not even until the body is warmed or thawed.

Rigor is one of the least reliable methods for determining the time of death because it is extremely variable. Heat quickens the process, and cold slows it. Obese people may not develop rigor at all, and in thin victims it tends to occur rapidly. If the victim struggled before death and consumed much of his muscular ATP, the process also is hastened.

The stiffness associated with rigor can be “broken” by bending and stretching the corpse. This stretches and breaks up the muscle fibers. Once broken, rigor won’t return.

Getting the blues: Lividity

In movies, the dead are beautiful, with perfect makeup and not a hair out of place. Real corpses are considerably less attractive, in large part because of the dark, purplish discoloration of portions of the body that comes from lividity. Also called livor mortis or postmortem hypostasis, lividity can help determine the time of death and indicate whether a body was moved after death.

Lividity is caused by stagnation of blood in the vessels. At death, the heart stops beating and blood ceases to move. Stagnant blood goes where gravity leads it. A corpse lying on its back develops lividity along the back and buttocks. A corpse lying on its left side shows lividity along the downside of the left shoulder, arm, hip, and leg.

However, any part of the body that presses against a firm surface appears pale and is surrounded by the lividity. For example, a corpse lying on its back shows lividity along its entire lower surface except where the body actually made contact with the hard floor. The shoulder blades, buttocks, and calves show pale points of contact, because the weight of the body compresses the blood vessels in these support areas and keeps stagnant blood from pooling. Tight-fitting clothing can do the same thing. A belt or brassiere can leave a pale track through an area of lividity.

The color of the lividity also can provide clues to the ME. Normal lividity is bluish or grayish in color, but red or pinkish lividity often is seen in deaths caused by carbon monoxide or cyanide poisoning or by exposure to cold temperatures after death. Alternatively, people dying from severe heart failure, shock, or asphyxia may develop deep purple lividity. The blood in these situations is usually poorly oxygenated and is thus deeply purple in color, which means any lividity also is deeply purple.

Lividity typically appears within 30 minutes to a couple of hours and reaches its maximum by 8 to 12 hours after death. During the first four to six hours after death, the discoloration can be shifted by rolling the body to a different position. When a body is supine (on its back) for a couple of hours and then rolled onto its left side, the lividity that began accumulating along the back shifts and begins accumulating along the left side. But after six to eight hours, the lividity becomes fixed because the blood vessels begin breaking down, and the blood escapes the confines of the blood vessels and settles in the surrounding tissues, permanently staining them. Moving the body after this does not shift the lividity.

The ME uses shifting and fixed lividity to estimate time of death and determine whether the body has been moved — something the dead don’t do without assistance.

The fixing process is not an all-or-nothing phenomenon. It occurs gradually, meaning that four to six hours after death, some of the lividity may be fixed and some still may be shifting. Whenever the ME finds that the corpse has some faint areas of fixed lividity along the back and true fixed lividity along the front, he may conclude that the body was lying on its back for four to six hours before it was moved and placed face down.

Of course, all these mental gymnastics presume normal circumstances. Because body decay and the breakdown of blood vessels depend primarily on the ambient temperature and because the fixing of lividity is caused by leakage of blood from decayed blood vessels, anything that hastens or slows the decay process has a similar effect on the fixing of lividity. In hot and humid environments, lividity may become fixed in as little as 3 or 4 hours, and in colder climates it can take as long as 36 hours.

Determining the rate of decay

The decomposition of the human body involves two distinct processes:

• Autolysis basically is a process of self-digestion. After death, enzymes within the body’s cells begin a chemical breakdown of the cells and tissues. As is true of most chemical reactions, the process is hastened by heat and slowed by cold.
• Putrefaction, which is a more destructive process, is caused by bacteria, which destroy the body’s tissues. The responsible bacteria come mostly from the intestinal tract of the deceased, but environmental bacteria and yeasts also may contribute.

Bacteria thrive in warm, moist environments but become sluggish in colder climates. Freezing stops their activities completely. A frozen body will not undergo putrefaction until it thaws. Occasionally the destruction of bacteria by freezing is so effective that putrefaction does not occur, and the body continues to desiccate, or dry out, a process that may lead to the eventual mummification of the body (see the section “Dealing with other possibilities” later in this chapter).

Dealing with other possibilities

Though the ME is most often confronted with bodies in various stages of putrefaction, decomposition is not the only way that a body can change after death. Under certain circumstances the following situations may occur:

• Mummification occurs when the body desiccates (dries out) in a hot, dry environment. Low humidity inhibits bacterial growth, and thus putrefaction, while at the same time sucking the moisture from tissues. In ancient Egypt, spices and salts were rubbed on corpses to hasten the drying process and ensure the bodies would mummify rather than decay. A leathery, dark-colored corpse results. The flesh looks like it was shrink-wrapped over the bones. Internal organs may dry and shrivel or become a dark, brownish-black, puttylike material. Mummified corpses tend to remain intact for long periods of time, which makes the determination of time since death difficult, if not impossible.

  The process of mummification actually is similar to the process of making beef jerky. In both situations, moisture is removed, causing drying (mummification) of the body’s tissues or the meat. Bon appétit!

• Adipocere formation occurs in very wet environments within the body’s adipose (fatty) tissues. The fat literally turns to soap. The result is a white, greasy, waxy substance. It gives the body an unreal, mannequin-like appearance. Adipocere formation most often occurs in bodies found in swamps, bogs, and other damp and acidic or alkaline areas. It takes at least three to six months to form, so a body with significant adipocere formation must have died several months earlier.

Bodies may not decompose uniformly, so a corpse may be found partially skeletonized and partially mummified or changed to adipocere. Incomplete embalming likewise can lead to partial preservation and partial skeletonization.

Breaking the surface: When sinkers become floaters

Bodies that die in water or are dumped into water shortly after death initially sink, but they eventually rise to the surface because of putrefaction gases that accumulate in the body’s tissues and cavities. The temperature of the water has a significant effect on how long this process takes. In the warmer waters of the Gulf of Mexico a body may float after only a few days or a week, while in colder waters 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 eight to ten days in warm water and after two to three weeks or more in cold water

Gazing into the eyes

After death, corneas — the clear coverings over your pupils — become cloudy and opaque. This process may take only a few hours if the eyes were open at death or up to 24 hours if the eyes were closed.

The concentration of potassium within the vitreous humor, the thick, jellylike substance that fills your eyeballs, increases slowly during the first few days. As opposed to many other postmortem changes, this process is independent of ambient temperature; however, any determination from vitreous potassium isn’t very accurate and is useful only within the first three or four days.

Discovering what was on the menu

The ME often uses the contents of the victim’s stomach to help determine the time of death. After a meal, the stomach usually empties itself in approximately two to four hours, depending on the type and amount of food ingested. If a victim’s stomach contains largely undigested food material, then death likely occurred within an hour or two of the meal, but this is extremely variable from person to person. If, on the other hand, the stomach is empty, the death likely occurred several hours after eating. Additionally, if the ME finds that the small intestine also is empty, death probably occurred at least 24 hours after the victim’s last meal. If the colon is empty, no food had been ingested for 48 to 72 hours before death.

These calculations depend upon a number of factors. Heavy meals and those that are rich in protein and fat digest more slowly than smaller meals and those that are high in carbohydrates and sugars. The consumption of alcohol and drugs, and even certain medical conditions, may affect digestion and gastric emptying. The rate of digestion also greatly varies from one individual to the next, which means that gastric contents are of only marginal help in determining the time of death.

Getting buggy

In addition to animal predators, numerous insects show up on a corpse to feast not only on the body itself but on other insects that are attracted to it. The ME uses these insects to aid in determining the time of death. Although bugs usually show up on a predictable schedule, these patterns vary greatly depending upon geographic region, locale, time of day, and season. Because of the complex nature of the bug world, the ME often asks for assistance from a forensic entomologist, who studies insects to uncover clues.

One example is the blowfly, which shows up early, often within the first hour after death. Blowflies seek the moist areas of the corpse to lay their eggs. The nose, mouth, armpit, groin, and open wounds are favored locations. Eggs hatch to larvae (maggots) within 24 hours. These larvae usually reach a length of a half-inch (one centimeter) after the first three days. During the next six to ten days the larvae feed, grow, and repeatedly molt, finally becoming pupae, when their outer covering hardens. Approximately 12 days later adult flies emerge, and the cycle continues.

In general and under normal circumstances, if the ME or entomologist finds only eggs, death likely occurred less than 24 hours earlier. If fully grown maggots but no pupae are found, death occurred less than 10 days earlier. Finding pupae indicates that six to ten or more days have passed, and the presence of mature hatchlings indicates that death occurred two to three weeks earlier.

Naturally, certain circumstances can throw off this schedule. Blowflies, for example, don’t deposit eggs at night and are less plentiful during winter. So, if the victim was murdered at midnight, blowflies may not appear until dawn, and if it’s cold outside, they may not appear at all. If conditions are unfavorable — extremely cold, for example — maggots may go dormant for extended periods of time. For example, if the body is in an area that’s warm during the day and very cold at night, maggots may be dormant during half of each 24-hour period. If it turns cold for several days, the developmental process may be put on hold during that time period. This can greatly complicate the determination of time since death.

Because the weather plays such an important role on the behavior of insects, the entomologist may also consult a climatologist. Information regarding the weather conditions during the past days and weeks can help the entomologist better understand his findings, which in turn helps the ME estimate the time of death.

Insect studies most often provide only a minimum time that’s elapsed since death occurred. Pupae cannot appear in fewer than six days, for example. To add to the confusion, insects appear in waves and new generations all the time. Adults produced after two weeks lay their own eggs, which then follow a similar cycle. So a three-week-old corpse may show fly eggs, maggots, pupae, and adults. I told you it wasn’t easy.

The ME collects live maggots, pupae, and empty pupal cases. Samples of the recovered maggots need to be placed in alcohol or a mixture of alcohol, kerosene, and other chemicals to preserve them in the state they were in when they first were observed at the scene. The criminalist may be asked to collect samples of the soil around the body to recover insects that pupate (develop) in the ground. The entomologist reviews all of the samples to determine

• The types of insects present
• Where each insect is within its developmental cycle
• How many development cycles have occurred

Checking other scene markers

The ME uses all the information at his disposal to estimate the time of death, including many nonscientific findings. Scene markers are any information found at the scene or taken from witnesses or family and friends. The last time the person was seen alive, for example, serves as a starting point for the ME. Family and friends can report the deceased’s habits and any changes they may have observed.

Missed work or forgotten appointments, not going on a regular daily walk or visit to the coffee shop, mail or newspapers left uncollected, and dated sales receipts all can be useful clues. Here are some examples:

• A broken watch or clock may indicate the time an assault took place.
• A victim who missed work for two days and is found at home, dressed in work attire and holding car keys, probably was heading to work at the time of death.
• A victim who never showed for a scheduled racquetball game and was found in the garage wearing exercise gear is likely to have died while leaving for the game.

Of course, the ME uses all the information from other parts of the investigation to confirm or refute this evidence.