A fact of life has always been death and for several millenniums humanity has observed certain physical aspects of death which occur in a predictable manner. This predictability has allowed humans to have tools to come to conclusions about how long a person has been dead. These conclusions take on special significance and importance when they are linked to homicides. The three classic tools are rigor mortis, livor mortis and algor mortis. Although utilizing these three tools have become more sophisticated in recent years, they are still primarily determined using a person’s senses (touch, sight, etc).
With the onset of death, the body’s normal functioning stops. Blood does not flow, oxygen does not reach cells and the chemical breakdown of the body begins. The three effects of death on a body begin. “The best known of the three, rigor describes the gradual muscle stiffening that grips a body in the hours after death and then melts away just as gradually. Algor represents the slow cooling of a warm-blooded corpse as it equilibrates with the temperature of its surroundings. The red-purple stain of livor, or lividity, documents the gradual settling of blood that begins the moment blood pressure plummets to zero.” (Sachs, 2001)
Although, these three indicators happen to each and every dead body, the accuracy with which one has been able to predict the time since death can be inconsistent due to the multitude of variables involved. The age, size and health of the person could change the rate of these three indicators, as does the environment in which the body is left. With the rise in technology these indicators can more accurately be measured but there is one other limitation. “Within twenty-four to forty-eight hours after death, lividity reaches its peak, the body reaches room temperature, and rigor disappears.” (Sachs, 2001) The homicide investigator therefore is left with no means with which to determine time since death of a body if it is found after these first crucial days, or is he?
In order to figure out other ways to determine the postmortem interval (PMI), one must understand what happens when we die. Just as rigor, algor and livor are all part of the death process other natural occurrences happen. In the cycle of life there is birth, life, death and decomposition. Decomposition is necessary for two reasons. First, the nutrients of one once living creature returns to the environment in order to provide nutrients for other living organisms, and second, to get rid if dead matter. If decomposition did not occur we would be left with a world covered in dead plants and animals.
Decomposition begins within the body. Even though one might be dead, our cells continue to function until they have exhausted their supply if oxygen and then they begin to cannibalize themselves, but this does not explain the complete process of the decomposition of a body. All dead matter needs a little help from nature and one of the most common, most abundant and fortunately for the homicide investigator very predictable helpers are insects.
A great many different species of insects play a role in the decomposition of bodies, whether they are murder victims or a forest animal that has succumbed to old age. Their roles happen to be at different times and they may be environmentally specific. One type of insect that homicide investigators have found to be particularly important are flies (the blue and green bottle flies, as well as, the blow fly being the most important) for two reasons. The first reason is that flies are found just about every where on Earth and the second is that they are usually the first to arrive on the scene.
The mere abundance of flies means that specialists can use their knowledge of the fly life cycle across a wide range of territory and the fact that flies arrive first, that is, at the time of death, means they can provide a predictable means to determine time since death for investigators.
In order to use flies as an indicator of the postmortem interval, an understanding of the how’s and why’s of a fly’s life cycle is necessary. British entomologist Dr. Zakaria Erzinçlioĝlu has devoted his career to understanding the life cycle of various insects. The following is the life cycle of the blue bottle fly, order Diptera, one of the forensically important fly species. Most fly species follow similar life cycles.
“The life history of a bluebottle begins when the female fly finds a dead carcass or corpse, which it can detect from a very great distance…[T]he fly seeks out the moist areas of the eyes, nose, ears or mouth, or a wound, in which to lay its eggs…When it has found a suitable site, the fly will lay its eggs – up to 300 at one sitting. It can do this up to ten times…laying something of the order of 3000 eggs in total.
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After a day or two, depending on the prevailing temperatures, the minute first-stage larvae will hatch…After another day or two, they shed their skins and turn into second-stage larvae, which themselves, after a similar period or time, moult to become third-stage larvae…They will feed voraciously upon the tissue for several days and grow to many times their original size…[M]aggots…can grow to six or seven times their original size…When the maggots finish feeding…[they] leave the body…[T]hey move far from the corpse to pupate…Normally, the maggots burrow into the soil and pupate below the surface.
Once the maggot has settled into its pupation site, its skin will begin to contract, harden and darken to form a structure known as a puparium or pupal case. Inside this shell, the tissues of the maggot begin to rearrange themselves…The pupa slowly forms and turns into the adult. The whole process takes about two weeks, at the end of which the adult fly emerges…” (Erzinçlioĝlu, 2000)
“A newly emerged fly cannot, in fact, fly. Its wings are crumpled and take time to expand and harden.” (Erzinçlioĝlu, 2000) Once the female adult fly can fly she must feed in order to develop her eggs. Once they are developed she must find another corpse on which to lay her eggs beginning the cycle once more.
As with any life cycle the order of stages remains the same whether the bluebottle is in New York City or the rural countryside of Oklahoma. The forensic entomologist though must be aware of those conditions which can change the time between stages. Various factors can speed up or slow down the development of the individual instars (stages) and so the forensic entomologist must be aware of all the variables of a crime scene and their likely effect before determining time since death.
Before looking at the variables that must be studied in determining the postmortem interval it is important to see how using insects in homicide investigations is nothing new. The earliest known use of insects in solving a homicide case can be found in a Chinese manuscript called The Washing Away of Wrongs (13th century). The death investigator, Sung Tz’u, describes various ways to “ascertain time of death in each of the four seasons.” (Sachs, 2001) This manuscript was meant to be a teaching manual for other investigators.
Tz’u describes one case in which a farmer is killed. The fact that the body was extensively wounded and the farmer’s possessions were not taken leads the investigator to suspect this was caused for personal reasons and therefore committed by an enemy, but no known enemies were found. Figuring that the perpetrator was someone from the village, the investigator ordered an examination of all the sickles in the village. Once all the sickles were laid out the investigator observed how after a time flies began to gather on one particular sickle. (Sachs, 2001)
The investigator confronted the owner of the sickle who at first denied having anything to do with the crime, but the investigator explained his reasoning, “‘The sickles of the others in the crowd have no flies…Now you have killed a man…so the flies gather.'” (Sachs, 2001) The flies presumably sensed traces of blood on the murder weapon. The farmer confessed to his crime.
Albeit, the use of flies in this case was not about determining time since death it does reveal the very close relationship flies and the dead have. In another historical example, insects become the key in determining the postmortem interval which is critical in pointing to one of several suspects.
The first appearance of forensic entomology being used in a Western court was in France, 1850. The mummified remains of an infant were found in a chimney of a boarding house when the building was undergoing plaster repairs. The couple living in the flat with the chimney was automatically accused of the murder, but they professed their innocence.
The flat had had no less than four separate couples residing in it over the past three years. Any of these couples could have been the murderers and therefore establishing the time since death was very important in determining which couple were the likely perpetrators.
Dr. Marcel Bergeret, a naturalist, who had been called in by the medical examiner “realized he might be able to construct a time line using the insects he’d collected from the body.” (Sachs, 2001) He determined the season of the infant’s death based on the remains of certain insects found on the body known to be active only at certain times of the year; in this case it was during the summer. He also determined that at least “two generations of insects were found in the corpse, representing two years postmortem.” (Sachs, 2001) Based on these conclusions the investigators arrested the couple who had lived in the apartment two years earlier during the summer.
Despite the good doctor’s ultimately unsophisticated methods for coming to his conclusions, the success and publicity of the case caused an interest in what would become forensic entomology. It would take another century, though, before forensic entomology would become a more common part of the investigative process.
The actual study of insects has been around for more than several millenniums. In fact Aristotle, one of the fathers of philosophy, took time to study insects more than 3000 years ago. Who Sachs, 2001 quotes as saying, “‘Some creatures come into being neither from parents of the same kind nor from parents of a different kind, as with flies…Such are all that come into being not from a union of the sexes, but from decaying earth and excrements.'” from his De Generatione Animalium. Despite Aristotle’s rather naïve belief (by today’s standards) of spontaneous generation he certainly understood the link between flies and decay.
Today’s scientific methods have certainly come a long way from Aristotle’s simple observations and the life cycle of not just flies but all manner of creatures can be measured and explained. Despite this understanding, the forensic entomologist must keep many things in mind. Murders can happen anywhere and at any time. Such conditions as the weather, environment the body is left in (inside or outside; on dry land or wet; buried or not) will all have an effect on the flies who come to lay their eggs, and on the larvae that are a result of those egg.
Forensic entomologists use the progress in the development of a fly species found in a homicide victim to determine how long the body has been exposed to maggot activity. Although flies have an uncanny knack for finding the recently deceased, there are many reasons for why flies may not actually begin laying eggs right away (the body may be in a shut off room, a bag, car or any container that may restrict flies from laying eggs right away) and therefore what is actually being calculated is the minimum postmortem interval, that is the shortest amount of time the victim could have been dead.
For the forensic entomologist to determine the progress of the larva’s development, she must know at what temperature the larva were bred at. In general, higher temperatures speed up development and lower temperatures slow it down. In order for the forensic entomologist to realize the role that temperature has played in the development of the larva in question “a record of ambient temperatures is routinely obtained from the weather station nearest to the body discovery site. However, there may be significant differences between the temperatures experienced at the site and the station…Therefore, many practitioners measure discovery site temperature for a period.” (Archer, 2004) The temperature from the site and the weather station are compared to each other so that some sort of mathematical relationship can be distinguished.
Once a reasonable estimate for the average temperature has been determined the forensic entomologist can then use one of two methods to determine the PMI. The first is to use the size of the larva. The length can be compared to published work which charts developmental length to temperature. (Ames and Turner, 2003) There are limitations to this approach such as determining the actual length of the larva (most specimens are killed during collection or are discarded casings which may lead to inaccurate measurements) and the need for the published work which is not extensive. Even though certain species are commonly found on corpses, they are certainly not the only ones likely to be present and the work to chart developmental rates is very time consuming and ultimately limited. “The other approach is to measure the accumulated degree days or hours (ADD or ADH) needed to reach a particular stage of development.” (Ames and Turner, 2003)
Accumulated degree hours is a mathematical approach that takes the number of hours a larva needs to develop at known temperatures and converts the actual hours from the actual temperature. “In other words, if a given insect species takes 100 hours at 10 degree Celsius (50 degrees Fahrenheit) to reach second-instar, it will take fifty hours at 20 degrees Celsius (68 degrees Fahrenheit)…One had only to be careful that temperatures remained within the insects’ minimum and maximum thresholds for growth.” (Sachs, 2001) It is important to mention here that a maggot population feeding can actually produce its own heat, and can distort results especially if the environmental temperatures appear to have gone low enough to slow development.
Temperature can play other significant roles in determining the minimum PMI. In general, flies are not active at night due to the coolness, therefore a body may lie exposed for the hours of night with no fly activity until the dawn and the warmth of the sun. Although this is a general rule, it is not an absolute rule and so all conditions of the site must be taken into consideration.
Another way in which temperature may skew the time since death determination is during times of extreme cold. Two things can happen with low temperatures, first flies will not lay eggs and will wait until things warm up such as in the night and day scenario which means the PMI may be thrown off by several hours (as the PMI is usually a range of days this may not be a significant amount of time for the over all investigation). Second, the cool temperature may last long enough to not only prevent fly activity but also to prevent immediate decay of the body. Once the body has thawed and the flies become active the PMI may be thrown off by a matter of days or weeks. It is important to mention that flies will only lay eggs on a “fresh” body, if decomposition goes past a certain point before flies can reach it they will not lay eggs. It is the nutrients of the once living flesh that the larva feed off of and so if there are no nutrients the flies will go elsewhere to lay their eggs.
Closely linked to temperature is whether or not a body is found indoors or outside. As people usually live and work in climate controlled environments the temperatures indoors may be very different from those outside. Flies which may not normally be active during a certain time of year may actually be found indoors.
In addition to the obvious link in temperature the indoor environment has the not so obvious link to access. As everyone knows insects in general and flies specifically have an annoying habit of getting into places where they are not wanted. But, most people do not stop to consider how long it took that fly to get into our homes. The forensic entomologist though must do exactly that. Again, it is important to remember that the PMI the forensic scientist is coming up with is a minimum time range. A well sealed room may have held off fly activity for sometime. A well sealed room may also confuse the issue by allowing several generations of fly larva to feed off of the same corpse (this is not unique to corpses found indoors but can also be an aspect of corpses found outside as well).
Corpses exposed to the elements have their own set of unique problems. The more exposed the body is the more exposed the larva are. As mentioned above flies are only one of a series of insects which take part in the decomposition of the body. Some of these insects come to feed off the larva themselves and can distort the PMI determination.
Some murderers make attempts to hide their crimes by hiding the body while others make no attempt to conceal their crimes at all. The manner in which a murderer leaves his victim can affect the insect fauna which results. An exposed unburied body will have the greatest access to insects and other non-insect scavengers. These circumstances cause the quickest decomposition of the body.
A shallow grave (which is the most common type used in the attempt to cover up a homicide) will attract different types of insects including hleomyzid flies that “will often lay their eggs on the surface of the soil above a buried body. Unlike most other corpse-breeding flies, the hatching larvae will burrow into the soil to reach and feed upon the body.” (Erzinçlioĝlu, 2000) Even though some species have specialized to be burrowing insects even regular fly species will be induced to lay their eggs over a buried body if the presence of blood can guarantee the female fly the likelihood of a nutrient source for her eggs. (Erzinçlioĝlu, 2000) The fact that the larva must burrow to their feeding source can delay the process of development affecting the PMI.
Another common dumping site is to submerge the body in water. As a body decomposes, a build up of gases causes the body to expand and if it is in water to float. Even though the insects of decomposition are not aquatic creatures they will take any opportunity to invade a body even if it is partially submerged. A water grave can affect the PMI in the fact that access to the corpse may not have been immediate. It may also affect the progress of development in terms of how much of the body is available to the insects. As water levels rise and fall depending on the seasons this can change the progress of insects. A rise in water levels can wash away insect activity or a fall in water level can begin a new cycle leaving two development process time tables on the same body which could cause confusion in determining the time since death.
Even if a forensic entomologist approaches a crime scene with a systematic approach and is able to take into consideration all the variables present at the scene the PMI determination can still be problematic. As was mentioned, the time since death range is exactly that, a range of time. The range given is usually several days long if not several weeks. This range can certainly be helpful in narrowing down a list of suspects or even in helping determine possible victims, as police can look for missing person’s reports from a certain time period. But in some cases a more precise time since death is necessary to establish the guilt or innocence of a particular suspect. In general, forensic entomology cannot provide this precision.
Scientists across the US and through out the world have been studying the effects of insects on decomposing bodies (pig carcasses are a common substitute for human bodies, but several studies use human cadavers) in a multitude of scenarios in order to more fully understand the process and in an attempt to provide more precise PMI determinations. Even if the postmortem interval can become more precise, it can still only be a minimum time since death. As murders do not happen in a lab setting, conditions can prevent immediate insect infestation.
Just as forensic entomologists are continuing to enhance their techniques other forensic scientists are enhancing the techniques within their own specialties. One example of what other scientists are doing is Arpad Vass whose chemical study of the compounds around and beneath a body is suppose to be another way to determine time since death. Vass found that “the ratio of compounds continuously evolved as the bodies decomposed further and further.” (Bass and Jefferson, 2003) It is Vass’s hope to be able to track these chemical progressions to come up with an exact time since death as the chemical breakdown of a body begins immediately.
Jason Byrd, on the other hand, has taken his own entomological expertise and joined forces with other forensic science disciplines such as botany and anthropology. He believes that where as “No one of these sciences could reliably predict time of death in all, or even most, circumstances…taken together, their individual contributions could weave a telling tale.” (Sachs, 2001)
As more and more scientists understand the natural life which surrounds death, forensic scientists will be able to provide information to investigators which will provide them with the circumstances surrounding a victim’s death. “When the German naturalist Ernst Haeckel coined the term ecology in 1869, he described it as the holistic study of living systems interacting with their environment. Ecologists look at communities of organisms, patterns or life, natural cycles, and population changes. And that is precisely what a new generation of forensic entomologists, botanists, and anthropologists have begun to do.” (Sachs, 2001) It is the ecosystem of the corpse they are studying in all its intricacies. And it is through an understanding of all the aspects of this system which will help lead forensic scientists to a more precise postmortem interval determination.
Works Cited:
Ames, C. and B Turner. “Low temperature episodes in development of blowflies:
implications for postmortem interval estimation.” Medical and Veterinary Entomology. 2003. Vol 17. 178-186.
Archer, Mel S. “The Effect of Time After Body Discovery on the Accuracy of
Retrospective Weather Station Ambient Temperature Corrections In Forensic Entomology.” Journal of Forensic Sciences, (May 2004), Vol 49, No 3, 553-559.
Bass, Bill, and Jon Jefferson. Death’s Acre: Inside the Legendary Forensic Lab the Body
Farm Where the Dead do Tell Tales. New York: G.P. Putnam’s Sons. 2003.
Erzinçlioĝlu, Zakaria. Maggots, Murder, and Men: Memories and Reflections of a Forensic
Entomologist. New York: Thomas Dunne Books. 2000.
Sachs, Jessica Snyder. Corpse: Nature, Forensics, and the Struggle to pinpoint Time of
Death. New York: Basic Books. 2001.
