Imagine you were in a fight to the death. Imagine that your opponent bit you during this match. Imagine that you lost‚ and that for some reason‚ the victor decided to bite your lifeless body again. Have you ever wondered if a bite mark made before death looks any different from one made after death? U of T graduate student Sylvie Louise Avon asked just that question‚ and what she’s finding out could make the difference between prison and freedom for untold numbers of innocent people.
“Pathologists assume when they see a bruise that it was made before death‚ but there has never been any research done that proves that one can tell if a mark was made before death or after death‚” said Avon. This seemingly minor detail could be crucial in court‚ and Avon set out to study the subject.
Her method of investigation: biting pigs.
“Pig skin is the closest animal equivalent to human skin‚ histologically‚ physiologically‚ and immunologically‚” said Avon. So she decided to inflict bite marks on a juvenile Yorkshire pig at four different time intervals—one hour before death‚ five minutes before death‚ five minutes after death‚ and one hour after death‚ to see if any difference could be seen between the bite marks. But what to bite the pig with?
“We had to design an appliance to inflict a bite mark‚ because I certainly didn’t want to bite the pig myself. We also wanted to make sure the bite would be consistent each time‚ so we needed an appliance to control the pressure accurately.” The result: a device flown in from the Bureau of Legal Dentistry in British Columbia known as the Bite–O–Matic. It consists of an upper and a lower set of chrome–cobalt teeth attached to a vice grip‚ with a detector connected to measure the pressure of the bite delivered.
Avon bit her pig at the stated time intervals on both the left and right sides. After killing the animal‚ she laid the pig on its side‚ as a murder victim might lie. “After you die‚ blood sinks to one side of your body under gravitational force‚” she explained. The side that the blood flows towards is known as the dependent side‚ and the side that the blood flows away from is known as the non–dependent side.
Avon found that bite marks could only be seen on the non–dependent side‚ and the clearest marks were those made five minutes before death‚ followed by five minutes after death‚ followed by one hour before death.
While that confirmed Avon’s suspicion that bite marks made before death may not be clearer than marks made after death‚ Avon discovered something else that shocked her: The bite marks weren’t bruises.
For a mark on someone’s skin to be technically considered a bruise‚ blood vessels need to be broken and blood cells released into the surrounding tissue‚ where they form immuglobin and eventually degrade. “”When I looked at the bite marks under the microscope‚ I was surprised to see no red blood cells at all.”” said Avon.
In other words‚ Avon has discovered that red marks on one’s skin may not necessarily be caused by blood‚ and this finding did not shock her alone. “I did a presentation of my results to a committee‚ and the director of the morgue at the coroner’s office‚ a pathologist‚ said flatly ‘That’s impossible.’ I asked him if he wanted to see the slides‚ and he said yes. So I left him with the slides by himself so as not to influence him. I waited in another room for half an hour‚ after which time he came back and simply said ’I don’t understand!’”
What could cause a red mark on one’s skin‚ if not blood? “I have a theory‚” said Avon‚ “but I can’t say. We’re now continuing the project‚ to test my theories.” Avon is optimistic about her continuing research. “I’m onto something!” she said happily.
Avon is also challenging another accepted concept in forensic science: the current practice of matching bite marks to suspects’ dental patterns. “In a court of law‚ it’s generally accepted that the dentist is correct because they are considered to be an expert witness in the field. But there is no conclusive scientific proof to date that a bite mark can be identified for a particular suspect.” So in phase two of her research‚ Avon will be biting three pigs with three different sets of teeth‚ and then sending photos of the bite marks along with moulds of the teeth to more than thirty experts around the world‚ asking them to match the bites to the teeth.
“I can’t wait to see the examiner’s results‚ because if they can’t show themselves to be reliable then that proves our current system of forensic investigation is flawed.” said Avon. She continues her research this fall.