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Finding the Cause of Death using Forensic Entomology

Posted in Forensic Entomology & DNA Barcoding by paibiopai on November 20, 2009

In a crime investigation, there is not only of great interest to find out when a victim died, but also of interest to find out how the victim died, as this can be used to find the killer.

In some instances the insects themselves are the killers, in other instances the insects occuring on the carrion can shed a light on what happened when the victim died.

Wasps and bees, for example, can inject venom through a sting. Some people are sensitive and allergic to these venoms, and can die if not treated in time. One other important aspect of wasps and bees are their effect on drivers. Many car accidents are probably caused by some wasp, bee or bumble-bee coming through the window, causing hysteria, or a distraction from the road leading to a collision or other accidents. In some cases wasps and bees has been used as murder weapons,  as in case where some parents had shut their infant in a room full of wasps, in order to get rid of it.

Poison can be traced in blood, urine, stomach contents, hair and nails. One other important source is maggots occuring on a corpse. After a while it will be impossible to sample stomach contents, urine and blood from the dead body, but it will still be possible to sample from maggots, empty puparia or larval skin cast. The following list of chemicals has to my knowledge been traced in maggots:

  • Triazolam
  • Oxazepam
  • Alimemazine
  • Chloripriamine
  • Phenobarbitol
  • Malathion
  • Mercury
  • Amitriptyline
  • Nortriptyline
  • Cocaine
  • Phenycyclidine
  • Heroin

Many of these chemicals will also influence the life-cycle of the maggot. For example will high dosages of cocain accelerate the development of some sarcophagids. Malathion, an insecticide, is commonly used in suicide, and is usually taken orally. Presence of malathion in the mouth may lead to a delay in the colonisation of the mouth. Presence of amitriptyline, an antidepressant, can prolong the developmental time with up to 77 hours, at least in one species of Sarcophagidae. Knowledge of drug use in the victim is therefore important not only in finding the death cause, but also in estimating the time of death.

The sites of blowfly infestation on the corpse may be important in determining the cause of death, or at least in reconstruction of events prior to death. For example: if there have been trauma or mutilation of the body prior to death, this may lead to heavy infestation of other body parts than the usual sites when the victim is not mutilated. Under a knife attack, it is usual to guard oneself with arms in front of thorax and head. This may lead to injury on the lower part of the arm. After death, blowfly may oviposit in these wounds.

The usual sites of oviposition on dead humans are natural openings. Even here there is preference. Blowflies will most often lay their eggs in the facial region, and more seldom in the genitoanal region. If there is a sexual assault prior to death, leading to bleeding in the genitoanal region, blowflies will be more likely to oviposit in these regions. Therefore, if there is observed blowfly activity in the genitoanal region, one can start to suspect a sexual crime. This must of course be corroborated with other evidence as well. The interpretation of maggots in the anogenital region becomes very fuzzy after a few (4-5) days, as eggs will be oviposited in this region during the course of decay in the natural course of decomposition.



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