Fire can't destroy all evidence

May 13, 2004, vol. 30 no. 2
By Marianne Meadahl

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Murderers who set fire to their victim's homes may think that they are destroying evidence. Forensic entomologist Gail Anderson has discovered otherwise.

In fact, even if a house is totally burned to the ground, the insects and larvae that were originally attracted to the body still hold valuable information that can help pinpoint time of death.

“The murderer will often turn to arson in a bid to destroy the body and the evidence,” says Anderson. “We now know that there is still much to be gained from the crime scene even after fire has occurred.

“Even if the insects are killed, they remain largely intact. All stages of their development are identifiable. That means evidence exists for time of death analysis.”

Anderson was invited by Inspector John Amerongen of the Edmonton fire department to carry out a study during an exercise last summer involving a planned house burning by an Edmonton insurance company. She placed three pig carcasses in different rooms inside the suburban house.

Each of the carcasses (the dead pigs were obtained from a butcher) was inflicted with a simulated bullet wound and allowed to decompose. Insects were able to get into the house through a small access hole in a window screen.

On the day of the planned burn, fire crews were parked outside as one of the carcasses was covered in blankets, doused with gasoline and set on fire. A short time later the fire spread and was allowed to burn while crews waited an estimated amount of time equivalent to that of a neighbour discovering the smoke and calling 911.

The crews went in and worked to contain the fire, as they would in a real situation, although much damage occurred. Although more than 30 centimetres of debris had fallen over the carcass, Anderson was able to assess the area around the carcass and found it still surounded by insect and larvae, all dead but identifiable. All of the tiny bits of evidence were still intact.

A second fire was set with a match and newspapers in another room and a similar scenario unfolded. This time, not only were identifiable insects recovered, but some were still alive.

During a third blaze the house burned to the ground. Anderson found the third pig, which had been placed in a bathtub, in the overturned tub, in the basement, covered in more than a foot of insulation debris.

Under the carcass was an array of insects and larvae, all dead this time, but all intact.

Members of the Edmonton police DNA lab helped Anderson collect the tiny subjects. She has subsequently studied them and concluded that they hold their weight in golden evidence.

“This has huge implications for these kinds of murder cases. It shows that you can't ever really destroy a body or the insect evidence,” says Anderson, who has also buried pig carcasses in the ground and anchored them at sea to carry out her studies.

She presented her preliminary findings at the European Association of Forensic Entomology in London in April and will present the final data at the International Congress of Entomology in Brisbane, Australia in August.

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