Kiwi researchers take a bite out of crime

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Kiwi researchers have uncovered new CSI-style techniques of gathering bacteria from human bite marks, which could hold the key to identifying murderers and sex attackers.

Geoffrey Tompkins, a senior lecturer at Otago University's school of dentistry, said traditional evidence based on the shape and size of bites was increasingly challenged in court and the discovery could offer a new avenue for investigators.

"It appears that each person's mouth has a unique collection of bacteria with their own distinct genotype, so the bacterial DNA profiles could potentially be matched and used as evidence.''

The research was carried out by students at the school of dentistry.

Dr Tompkins said a potential problem was that bacteria doesn't live long outside the mouth, but the study found the DNA of dead bacteria can be recovered from bite marks to produce DNA profiles.

"It's very accurate,'' he said.

Environmental Science and Research (ESR) forensic programme manager Jill Vintiner said she saw the potential for the new research.

ESR does not work with bacteria and usually matches bite marks with suspects through DNA left in saliva.

"Anything that assists an investigation and any new tool that gets developed is always a good thing,'' Dr Vintiner said.

But she said the research would need rigorous reviews before it could be used to convict New Zealand criminals.

"There's a huge amount of work that goes on before you can start new techniques because at the end of the day if you're in court you need to be able to stand by your result and your work.''

An editorial in the Journal of the American Dental Association said bite marks typically occur during violent assaults, homicides and abusive domestic situations.

"Owing to the nature of the tissue, however, the resulting evidence may consist only of a bruise, scrape or laceration. Investigators then try to match the suspect's dentition with the pattern of the wound, attempting to identify or exclude a suspect.''

Although evidence about bite marks is accepted in the courtroom, research supporting analysis is "sorely lacking'', the journal said.

"Innocent people who have spent years in prison, some on death row, now are being released after examination of DNA evidence that positively excluded them as the perpetrator of the crime.''

For example, Robert Lee Stinson, convicted of murder on the basis of bite mark evidence, served 23 years in prison for a crime he did not commit before testing of DNA evidence set him free.

However, the importance of bite mark evidence was illustrated in the case of serial killer Ted Bundy.

"Although authorities had circumstantial evidence that placed Bundy at the scene of his last murder, it was the bite mark evidence that led to his conviction,'' the journal said.

"Without this evidence, he might have been free to commit more crimes.''

The Otago University research has been submitted to a scientific journal for publication.