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Lead Author: Kelsey Kramer
Crime solving Critters
Crime solving Critters
Bugs are controversial. Some people love them, some people hate them. We know that they are important to the environment and all, but they can be annoying, right? It may be time to set aside our differences with these little critters because they are crime solvers! Blowflies are used in cases involving deaths. Their development is used to determine the postmortem interval (PMI) or time since death. This measurement in incredibly important in suspicious death cases. Normally, the time of death is not known. This unknown can put a halt to the case, as potential alibis cannot be proven or disproven. Luckily for investigators, blowflies can give the time of death.
When using blowflies to determine post-mortem interval (PMI), understanding and predicting the blowfly’s life cycle is key. An adult blowfly will lay eggs on the deceased. From the time the eggs are laid to the time they become adult flies, they will go through predictable forms: three larval stages and a pupa stage. What are commonly called maggots are blowflies in one of the three larval stages! These are referred to as first, second, and third instars which differ greatly in size. After the maggots complete the third instar stage, they go into the pupa stage. The maggots will form a hard shell that encases them to incubate as they transform into an adult fly. These developmental stages follow a timeline, making them extremely predictable. There are, however, some variables that affect this timeline.
Two things that will greatly affect the development of blowflies are light and temperature. Forensic entomologists have done hours upon hours of research so they can further predict the outcome of these variables. These entomologists control the conditions of light and temperature, then closely study how the blowfly development is affected. This research has led to a wide range of data that can be used to determine the age of a blowfly at whatever stage it may be in.
These experiments have also led to what is called succession data. This data tracks the species that appear at the scene of a death. It records what order they show up in, when they come, and how long they stay.
Developmental data
Developmental data
Looking at the length and weight of larva collected from the scene, their age can be approximated. With this information, the PMI can be found.
Succession data
Succession data
Based on the amount and identity of the various species present on the scene, a post-mortem interval can be estimated.
These two types of data, development and succession, are what entomologists use to determine PMI. When using developmental data, the entomologist looks at the length and width of the larva, comparing it with a growth curve (shown in figure). The length and width are plotted along the curve and the time is found from there. To use succession data, a thorough account of what species are present, as well as their developmental stages, must be recorded at the scene. This is then compared to the studied succession patterns and a timeline can be established. Both these methods are used in real cases where the forensic entomologist testifies their findings in court.
case study
case study
In Clinton, Ontario, June 11th, 1959, a 12-year-old Lynne Harper was discovered dead in a woodlot. Insect evidence was collected and photographed at the scene and during the autopsy, but it was not used in the trial in 1959. The time of death that was originally placed was a 45-minute window around 7:00pm to 7:45pm on June 9th, two days before her discovery. This window was established via stomach content analysis. Based on this timeframe, 14-year-old Steven Truscott was convicted of her murder as he was determined to be the last person to see her alive. Truscott preached of his innocence in prison. In 2001, the case was appealed and reopened. In 2006-2007, new evidence was presented to the Ontario Court of Appeal in the form of 3 forensic entomologists. They re-created the crime via an experiment which proved that the initial time of death estimation was unreliable. The larva would have been much bigger if they were laid just before dark on June 9th. They were colonized during the daylight on June 10th. This information, along with witness testimony solidifying Truscott’s alibi for the 10th, was enough to overturn the conviction and acquit Truscott of the murder charges. This case is a prime example of why an accurate post-mortem interval is detrimental to a case.
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