Bitemark evidence can send wrong person to prison, death row, UB professors say

During a trial for murder or another violent crime in which a victim has been bitten, prosecutors may display photos of the bitemarks next to tracings of the suspect’s teeth. And the two may appear to fit perfectly. Case closed, right?

Not necessarily, according to Mary Bush, a forensic dentist and associate professor of restorative dentistry in the School of Dental Medicine. For years, Bush has maintained that human dentition is not unique with regard to bitemark analysis, and seemingly perfectly matching bitemarks could belong to a litany of suspects.

Bitemarks aren’t only inadequate, Bush says, but they also have been misused in courtrooms. In a commentary published in the May 2023 issue of the Journal of the California Dental Association, Bush pointed out that 26 people have been wrongly convicted primarily because of a bitemark found on the victim. At least three of the suspects ended up on death row.

Bush co-authored the article, “Bitemark Analysis: The Legal vs. Scientific Battle for Justice,” with Raymond Miller, clinical associate professor of dental medicine and a forensic dental consultant to the Erie County Medical Examiner’s Office, and Peter Bush, director of the South Campus Instrument Center and co-founder of the Laboratory for Forensic Odontology Research.

“The premise of bitemark analysis rests on two main assumptions,” Mary Bush explains. “First, that the arrangement of the human teeth in the mouth is unique, and secondly, that unique features transfer to the skin.”

She points out that problems typically arise when the jury is shown tracings of the suspect’s dentition and a photograph of the wound that fit reasonably well.

“They always do,” Bush says. “And once the jury sees that supposed ‘fit,’ it’s hard to unsee it. The question is: How many other people could have fit the bite? This, the jury does not know.”

Because a victim is usually struggling with the attacker in cases of assault or murder, the skin is moving and ends up bruised.

“In an actual bitemark case, a bruise, not indentations of teeth, is what is typically examined,” Bush maintains. “A bruise may create further uncertainty as it is diffuse and may not accurately reflect the tooth arrangements that created the wound.”

People assume that human dentition is unique because dental records are often used to identify the dead. However, in those cases, the combination of 32 teeth — present, missing and restored — are analyzed, compared with only the incisal edge of the six teeth that typically leave a bitemark, she notes.

“Courts are content to allow the evidence in and let rigorous cross-examination bring out any fault in the ‘science,’” Bush says. “This leaves it to the lawyers, who may not have a scientific background, to adequately cross-examine.”

Interestingly, Bush found that the teeth marks that fit best usually do not belong to the actual perpetrator.

While bitemarks have been used in criminal cases going back to the 1800s, they weren’t really relied on until the 1970s. One of the more famous cases was that of notorious serial killer Ted Bundy in 1979.

The prosecution had reams of circumstantial evidence tying Bundy to at least one of the many murders he was accused of committing. However, it was the teeth marks found on one of his victims that eventually sealed Bundy’s guilt. He was convicted of first-degree murder, attempted first-degree murder and burglary. Later, Bundy confessed to killing 30 women between 1974 and 1978. This highly publicized case elevated the stature of bitemark evidence, Bush notes.

However, Richard Souviron, the forensic odontologist who testified at Bundy’s trial, recently said his bitemark testimony would have been different after 30 additional years working in that field.

The introduction of DNA into criminal trials has made a significant difference, Bush says, often knocking out bitemark evidence, though it’s still available in the prosecutorial toolbox.

“It isn’t so much that prosecutors are using bitemarks inappropriately,” Bush says. “There is simply a lack of awareness about how much distinction there could be in two sets of teeth.”

Bush never intended to wade into the contentious waters of bitemark analysis. She only got involved in 2006 when one of her students chose bitemarks as an area of forensic dentistry he wanted to study. As part of the student’s research, they took a mold of Bush’s teeth and made bitemarks on 23 cadavers.

“We then photographed the bitten body part in varying positions to examine the effect of movement,” she says. “It stands to reason that an altercation of a body part may be bitten in one position, but examination of the mark is conducted while the body part is in another.”

Of the 23, none was measurably identical to each other.

They conducted subsequent studies, including geometric morphometric analysis, which can quantify shape change variation between large datasets. Again, they made multiple bites with the same set of teeth and determined that the bites did not transfer to the skin in a reliable fashion.

Bush and her team also testified at a hearing before the Texas Commission on Forensic Science in 2015 and the President’s Council for Assistance in Science and Technology in 2016.

The Texas commission ruled on Bush’s side, recommending the state issue a moratorium on the use of bitemark analysis in prosecutions throughout the state. The president’s council also advised against using bitemark evidence, providing the conclusion that “the prospects of developing bitemark evidence into a scientifically valid method are low.”

And in October 2022, the National Institute of Standards and Technology published its findings in a draft report, “Bitemark Analysis: A NIST Scientific Foundation Review,” stating, “Forensic bitemark analysis lacks a sufficient scientific foundation because the key premises of the field are not supported by the data.”

Despite these official findings, the practice of introducing bitemark evidence to juries has not ended.

“To my knowledge, there are no courts where bitemarks aren’t allowed as evidence, Bush says, “though there are some that don’t use it.”

By increasing awareness and helping lawyers and the general public understand the limitations of bitemarks and how they can be skewed, Bush hopes false convictions hinging on this flawed evidence eventually will be eliminated.