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The American carrion beetle, Necrophila americana.  Although this beetle is primarily nocturnal, it is commonly observed on the upper surfaces of a body during the daylight hours.  Large aggregations of these beetles have been observed, and they can sometimes be as numerous as flies.

Forensic Entomology

Forensic Entomology is the use of the insects, and their arthropod relatives that inhabit decomposing remains to aid legal investigations.  The broad field of forensic entomology is commonly broken down into three general areas: medicolegal, urban, and stored product pests.  The medicolegal section focuses on the criminal component of the legal system and deals with the necrophagous (or carrion) feeding insects that typically infest human remains. The urban aspect deals with the insects that affect man and his immediate environment. This area has both criminal and civil components as urban pests may feed on both the living and the dead. The damage caused by their mandibles (or mouthparts) as they feed can produce markings and wounds on the skin that may be misinterpreted as prior abuse. Urban pests are of great economic importance and the forensic entomologist may become involved in civil proceedings over monetary damages.

Decomposition - is the process whereby bodily tissues are broken down into smaller molecules after death. The physical and chemical properties observed during decay are categorized into five stages: (1) fresh, (2) putrefaction, (3) black putrefaction, (4) butyric fermentation, and (5) dry decay

Time of Death

General factors used to estimate time of death are:

Body temperature, rigor mortis, postmortem lividity, appearance of the eyes, stomach contents, stage of decomposition and evidence suggesting a change in the victim’s normal routine.

Body Temperature:

• drops 2 to 3 degrees in the first hour after death; and 1 to 1.5 degrees for each subsequent hour up to 18 hours

Rigor Mortis:

• appears in the head 5 to 6 hours after death; in the upper body after about 12 hours; and in the entire body after about 18 hours.
• after about 36 hours, rigor mortis usually disappears in the same sequence that it appeared. 
• any weapon tightly clenched in the victim’s hand as a result of cadaveric spasm indicates suicide rather than murder

Postmortem Lividity:

• starts one half to 3 hours after death and is congealed in the capillaries in 4 to 5 hours
• maximum lividity occurs within 10 to 12 hours
• the location of lividity can indicate whether a body was moved after death

Eyes:

• partial constriction of the pupil occurs in about 7 hours
• in 12 hours, the cornea appears cloudy

Stomach Contents:

• the investigator should determine when and what the victim last ate - if any vomit is present, it should be preserved as evidence and submitted for examination

Water:

• a dead body usually sinks in water and remains immersed for 8 to 10 days in warm water, or 2 to 3 weeks in cold water - it them rises to the surface if not restricted
• the outer skin loosens in 5 to 6 days, and the nails separate in 2 to 3 weeks

Rigor Mortis (latin: stiffness after death)

Caused by a chemical reaction in the muscles after death

a good determination of the time of death - it begins a few hours post-mortem, reaches it’s maximum at about 12 hours, and then gradually decreased for about 3 days. Environmental factors, such as temperature, can speed up or slow down the process.

Forensic Entomology

Forensic Entomology is the use of the insects, and their arthropod relatives that inhabit decomposing remains to aid legal investigations.  The broad field of forensic entomology is commonly broken down into three general areas: medicolegal, urban, and stored product pests.  The medicolegal section focuses on the criminal component of the legal system and deals with the necrophagous (or carrion) feeding insects that typically infest human remains. The urban aspect deals with the insects that affect man and his immediate environment. This area has both criminal and civil components as urban pests may feed on both the living and the dead. The damage caused by their mandibles (or mouthparts) as they feed can produce markings and wounds on the skin that may be misinterpreted as prior abuse. Urban pests are of great economic importance and the forensic entomologist may become involved in civil proceedings over monetary damages.

http://www.forensicentomology.com/definition.htm

Time of Death

General factors used to estimate time of death are:

Body temperature, rigor mortis, postmortem lividity, appearance of the eyes, stomach contents, stage of decomposition and evidence suggesting a change in the victim’s normal routine.

Body Temperature:

• drops 2 to 3 degrees in the first hour after death; and 1 to 1.5 degrees for each subsequent hour up to 18 hours

Rigor Mortis:

• appears in the head 5 to 6 hours after death; in the upper body after about 12 hours; and in the entire body after about 18 hours.
• after about 36 hours, rigor mortis usually disappears in the same sequence that it appeared. 
• any weapon tightly clenched in the victim’s hand as a result of cadaveric spasm indicates suicide rather than murder

Postmortem Lividity:

• starts one half to 3 hours after death and is congealed in the capillaries in 4 to 5 hours
• maximum lividity occurs within 10 to 12 hours
• the location of lividity can indicate whether a body was moved after death

Eyes:

• partial constriction of the pupil occurs in about 7 hours
• in 12 hours, the cornea appears cloudy

Stomach Contents:

• the investigator should determine when and what the victim last ate - if any vomit is present, it should be preserved as evidence and submitted for examination

Water:

• a dead body usually sinks in water and remains immersed for 8 to 10 days in warm water, or 2 to 3 weeks in cold water - it them rises to the surface if not restricted
• the outer skin loosens in 5 to 6 days, and the nails separate in 2 to 3 weeks

Forensic Entomology

Forensic entomology is mainly used during the investigation of murders and is the use of insects found on and around the body to determine an approximate time of death.  Considerable research has been done at “The Body Farm” in Tennessee surrounding the decomposition of bodies after death in various conditions.  Among this research is the timing of insect arrival at the body and the development or maturation of the insects over time, in various temperatures, and in comparison to the decomposition of the body.

When an individual dies, the arrival of insects begins very rapidly, and when the individual is a victim of a violent crime where there is blood, urine, or semen present, insect activity may begin immediately.  Blow flies are most often attributed to the use of entomology for identifying an approximate time of death because they go through their life cycle in a fairly predictable pattern, which is dependent upon temperature.  Therefore, when an entomologist attempts to determine an estimated time of death, they must also take into account the weather patterns.  Most people are familiar with blow flies if they have ever went to a location where there is a public garbage on a hot summer day.  Blow flies like to lay their eggs on or near a food source, which can be rotting garbage, vegetation, manure, and in the case of crime scenes, dead bodies.  Open wounds are a preferred site for laying eggs, however, mouths, noses, and genitals may also be a site. 

After the eggs are laid on or in the body, they tend to hatch quite rapidly and become maggots, which begin to consume the body.  Again, depending upon temperature, maggots can pupate and become adults within a few days, in fact, the entire cycle from egg to adult can occur in a week.  Armed with the expert knowledge of insect life cycles, the forensic entomologist will collect a sampling of all stages of development and can then provide an estimated time of death.  Insects at the scene of a crime can also provide information about whether a body was moved, if there are poisons present and if the victim has been intoxicated with drugs or alcohol.

Determining Time of Death 

Determining time of death is not as easy as it looks on television. Investigators use what is called the “Time of Death Certainty Principle”.

“If you know with certainty when the person was last known to be alive, and if you know with certainty when they were found dead, then you know with 100% certainty that they died within that interval.”

While that seems rather simple, it is a starting point. Once this interval of time is determined other methods can be used to further try and pinpoint time of death.

Medical Indicators of time of death:

There are changes that occur after death. Most of them are chemically related. Blood settles by gravity within the body, and there’s a purple discoloration that occurs — that’s called lividity. The body will become rigid. That’s called rigidityor rigor … People have looked at vitreous humor, which is the fluid in the eye; the corneas become cloudy … You can look at the gastric contents [food left in the stomach or intestines]. You know, when did they last eat, and that can be helpful. Do they have a full bladder or not?

All of these recognized chemical changes associated with death happen at intervals of time that are widely known. But these are not airtight indicators. Variables like ambient temperature, chemicals in the blood stream and other factors can affect the rate at which these changes occur.

Non-medical indicators of time of death:

This includes things such as when did they last pick up their mail, when did the voice mail/answering machine start picking up all their calls, when did they last log onto their computer.

Forensic entomology has also become extremely helpful in helping to determine cause of death.