Chapter 11
IN THIS CHAPTER
Understanding the intricacies of timing death
Looking at physical changes after death
Using bugs and other telling evidence
A husband says that he left home for a business meeting at 2 p.m. and returned at 8 p.m. to find his wife dead. He says that he was at home all morning and that she was alive and well when he left. Maybe, maybe not, but establishing the wife’s time of death will refute or support his story. If the medical examiner (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 he has a reliable alibi for that time period, the investigation will move in a different direction.
In criminal cases, an accurate determination of the time of death eliminates some suspects and focuses attention on others. Determining the time of death, however, is an inexact art, and to make a best-guess estimate, the ME uses each and every means available, from witness statements to body temperature to (egad!) bugs on the body.
Time of death seems like a simple and straightforward concept. It’s the exact time that the victim drew a last breath, right? Wrong. Time of death actually comes in three different forms:
The only absolutely accurate determination of the time of death is under the uncommon circumstance in which a person dies with a physician or other skilled medical professional present. Many deaths, however, are not witnessed by anyone. Natural deaths may occur during sleep, and accidental and suicidal deaths often occur when the victim is alone. In homicides, the perpetrator typically is the only witness, and even if he checks his watch, he’s not likely to pass on that information.
After death, bodies begin to decompose, and they do so in a somewhat predictable pattern. The ME uses this pattern to estimate the physiological time of death. Unfortunately, these changes don’t take place within a rigid time frame, and they occur in widely variable ways. No single factor accurately indicates the time of physiological death. It’s always a best guess.
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.
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.
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 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:
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.
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.
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.
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.
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.
The decomposition of the human body involves two distinct processes:
Putrefaction is an ugly and unpleasant process. (The faint of heart may want to skip ahead to the next section.) Under normal temperate conditions, putrefaction follows a fairly predictable sequence:
As gasses accumulate, the abdomen swells, and the skin continues to blister. Skin and hair begin to slip from the body, and fingernails start to slough off.
If you were to pull on the body at this point, to move an arm, for example, you’d likely come away with a handful of skin instead.
Internal organs also decay in a known order, and the ME uses this pattern to estimate time of death. The intestines, which hold many bacterial species, decay first, followed by the liver, lungs, brain, and then the kidneys. Stomach decomposition is often delayed because the stomach may contain food mixed with a significant amount of acid that slows the growth of the bacteria and may even kill many of them. Lastly, the uterus or prostate succumbs to invading bacteria.
I told you it wasn’t pretty.
Environmental and internal body conditions can alter the process of decay. Obesity, excess clothing, a hot and humid environment, and the presence of sepsis can speed up the process so much that 24 hours can do the damage of five or six days. Sepsis is particularly destructive to the body, because not only is the body temperature higher at the time of death, but the septic process also spreads bacteria throughout the body.
Conversely, a thin, unclothed body lying on a cold surface with a cool breeze follows a much slower decomposition process. Very cold climes can slow the process so much that even after several months, the body appears as though it’s been dead only a day or two. Freezing protects the body from putrefaction only if the body is frozen before the process begins. Once putrefaction sets in, however, even freezing the body may not prevent its eventual decay. If frozen quickly enough, the body can be preserved for years.
Left unchecked, the decomposition process ultimately leaves behind only a skeleton. Obviously, the time required for a body to skeletonize is determined by the same conditions that dictate how fast putrefaction occurs. In a Louisiana swamp in August, the process may take only a week or two, but in February in Minnesota, putrefaction may be delayed until spring.
Estimating the time of death for a corpse that is more than a few weeks old is particularly challenging for the ME because body temperature, rigor mortis, and lividity no longer are of any use. What’s left? The expected stages of postmortem decay, but even that timeline must be modified according to the conditions at the site where the body is found.
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!
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.
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
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.
Determining the time since death is not an easy task, and every bit of information helps. The ME uses not only the above techniques but any other information he can glean from the body and from the site where it was found. Three very useful types of information include the victim’s stomach contents, the actions of various insects on the corpse, and materials found near the body.
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.
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.
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 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:
Of course, the ME uses all the information from other parts of the investigation to confirm or refute this evidence.