We are all dead.

We have exhaled the last breath. Our heart has stopped pumping blood for the brain and the body. We died.

Unfortunately, no one was with us when that moment came until now. Will the coroner and the medical examiner know when that particular moment happened? Yes.

How? They have the interval detectives.

Upon the discovery of human remains, the key question asked usually was the time of death. To answer that question, M.E. has to find out the postmortem interval (PMI), which is the amount of time has elapsed since the death.

Photo illustration by James Emmerman. Photo by Shutterstock

There are ways to do so. Recalling the decomposition schedule we discussed last time, in the first few hours, a lot of changes would happen: livor mortis (settling blood, algor mortis (cooling of body temp) and rigor mortis (stiffness). These methods usually able to accurately calculate the first, at most 24 hours interval. By the time the body starts decomposing, these would not work.

A lot of Medical Examiner would choose to use the drop of body temperature as a tool to get PMI. Average body (living body) temperature is about 37⁰C or 98.6⁰F. Under normal circumstances, at normal room temperature, the body would drop 1.5⁰C in the first hour after death, and between 1.5 and 1⁰C every hour after that, and stopped until it reached the room temperature. By comparing and calculating, it would allow the M.E. find the time of death. Yet, it does not work at best when the body starts decomposing.

A number of factors will affect the rate of the temperature drop. A naked body will be at a faster rate than a body that is wrapped like a gift. Also, body of lesser weight will enjoy the privilege of faster temperature drop too! If the body has been dead for days, looking into the past weather reports would help too.

Seems like everything does not work as well when the decomposition begins. Correct! But we are so lucky that the mother nature gives us our little death detectives– insects!

The application of insects or bugs science to investigation about crimes is called forensic entomology. Entomology, means the study of insects. The live and dead insects found at the site of crime can tell many things, from the crime scene, the length of time the body had been there, the time since death, and even if the victim being drugged.

After the rigor mortis is over, putrefaction begins. It is about the internal breaking down of the proteins in a decomp body. Acid like the gastric juice (Hydrochloric acid) starts eating the internal organ, releases gases (ammonia, nitrogen, carbon dioxide, and methane). They sometimes bloats the body cavity. As the decomposition goes, the odor would get stronger. That’s the odor cadaver dogs rely on to look for a body. Lately, an international research team measured the volatile organic compounds (VOCs) from pig carcasses, they identified a cocktail of several families of molecules. The found that the combination and quantities of the VOCs change as the body go through stages of decomposition. It worked as the “odor fingerprint” of decomp.

Insects then, particularly flies, begin feeding on remains. Studies show that flies are attracted by the released gas, and have a feast around the moist and opened tissues/ areas: eyes, ears, nose, mouth, vagina, penis, anus. If there are wounds (antemortem and perimortem), they would invite themselves into these areas too. As they continue to enjoy the feast, they reproduce. The deposit eggs in and around the remains, and starts a cycle of arthropod activity. The schedule is as follows (Bass 1977):

• First Day:  Egg masses of insects (may look like white sawdust); veins seen through skin may be blue or dark green; body fluid may be present around nose and mouth.
• First Week: Maggots are active on the face; bones around eyes and nose may be exposed; beetles may appear; skin and hair may slip from the body; remains emanate odor of decay; abdomen may be bloated; molds may begin appear on the skin; animals may be active. VOCs or Volatile fatty acids may killed the vegetation in area around the body.
• First Month: Maggot activity less, beetles more common; no more bloating. Bones will be expose if the body is shaded. Skin may be leathery if its exposed to sunlight, which protects the maggots from the sun. Mammalian carnivores may appear and remove body parts; molds can be found; adipocere (Grave Wax) may be present.
• First Year: Skeleton fully exposed and bleached; moss and/or green algae may be growing on shaded bones. rodent gnawing; animals may nest in the skull.
• First decade: Exfoliation of cortical bone may be present; longitudinal cracks may occur in long bones exposed to sun; roots of plants may be growing in or through bones.

“You are what you eat. So do the insects.”

As you may realize by now, the insects are entirely fed on the body. Entomologist by studying the living habit or the life cycle of the insects may be able to tell if the insects have intake some alternative materials from the body, such as necrotic. Likewise, insects can help clean the bones by having them eating up the soft tissue. These are the most convenient way to do if maceration is not on the top of your list.

Other than forensic entomology, forensic botany (the application of plant science to investigation about crimes) is also useful to map out the time elapsed since death. You may recognize in the above schedule, the plant would die out after the first week. The acids from the internal body would kill all the nutrients, acidify the soil, and make the soil is not suitable for plantation. However, later on, when the whole body started breaking down, the whole body is indeed some sort of organic nutrients. The decomposition of body thus can restore the nutrients into the acidify soil. Plants will grow nice and strong at the spot. Thus, abnormal plantation patterns may reflect the placement of dead body too. Plus, plants and roots would grow around the bones (as support sometimes).

A new finding from Forensic Biologist from Switzerland found that the density of testate amoebas in the soil underneath the cadavers help date older corps. The study finds that not one single living amoeba found be found under the cadavers at 22 and 33 days after placement, while only by day 64 the amoebas start to rebound in the soil under the pig. Yet, the level of amoebas did not restore to its normal level (according to the control) even after a year.

References:

Bass, W.M. (1997). Outdoor decomposition rates in Tennessee. In: Halgund, W.D., Sorg, M.H., eds. Forensic Taphonomy. New York: CRC Press.

Byers, Steven N.. (2011). Introduction to Forensic Anthropology. 4th edition. Upper Saddle River: Prentice Hall, pp. 94-111.

Frazer, Jennifer. (2014). “A Surprising Time-of-Death Tool.” Scientific American. September 16, 2014.

Knowles, Ruth. (2014). “Changing Smell of Corpses Measures Time of Death.” Scientific American. June 26, 2014.