In some suspicious death investigations, arthropod evidence may prove that the body was moved at some point after death. Crime scene insects can tell whether the body decomposed at the location where it was found, and even reveal gaps in the crime time line.
When Insects at the Crime Scene Don't Belong There
The entomologist first identifies all the collected arthropod evidence, cataloging the species present on or near the body. Not every insect belongs in every habitat. Some live in quite specific niches - on limited vegetation types, at certain elevations, or in particular climates. What if the body yields an insect that is not known to live in the area where it was found? Wouldn't that suggest the body had been moved?
In his book A Fly for the Prosecution, forensic entomologist M. Lee Goff tells of one such case. He collected evidence from a woman's body found in an Oahu sugar cane field. He noted that some of the maggots present were a species of fly found in urban areas, not in agricultural fields. He hypothesized that the body had remained in an urban location long enough for the flies to find it, and that it was later moved to the field. Sure enough, when the murder was solved, his theory proved correct. The killers kept the victim's body in an apartment for several days while trying to decide what to do with it.
When Insects at the Crime Scene Don't Fit the Timeline
Sometimes insect evidence reveals a gap in the time line, and leads investigators to the conclusion that the body was moved. The primary focus of forensic entomology is the establishment of the postmortem interval, using insect life cycles. A good forensic entomologist will give detectives an estimate, to the day or even the hour, of when the body was first colonized by insects. Investigators compare this estimate with witness accounts of when the victim was last seen alive. Where was the victim between when he was last seen and when insects first invaded his corpse? Was he alive, or was the body hidden somewhere?
Again, Dr. Goff's book provides a good example of a case where insect evidence established such a time gap. A body found on April 18th yielded only first instar maggots, some still emerging from their eggs. Based on his knowledge of this insect's life cycle in the environmental conditions present at the crime scene, Dr. Goff concluded that the body had only been exposed to insects since the previous day, the 17th.
According to witnesses, the victim was last seen alive two days prior, on the 15th. It seemed that the body must have been somewhere else, protected from exposure to any insects, in the interim. In the end, the murderer was caught and revealed he had killed the victim on the 15th, but kept the body in the trunk of a car until dumping it on the 17th.
How Insects in the Soil Help Solve a Murder
A dead body lying on the ground will release all its fluids into the soil below. As a result of this seepage, the soil chemistry changes substantially. Native soil organisms leave the area as the pH rises. A whole new community of arthropods inhabit this gruesome niche.
A forensic entomologist will sample the soil below and near where the body was lying. The organisms found in the soil samples can determine whether the body decomposed at the location where it was found, or prior to being dumped there.