In the 1980s, the community of Andalusia, a small town deep in Alabama, was shaken by the gruesome murder of Julie Bonds. The prime suspect was her husband, Charles McCrory, who was arrested and quickly put on trial. Although such tragedies are deplorable, they aren't exactly uncommon even in quaint, rural America. But what made this case truly exceptional and, honestly, outrageous was the testimony of one of the expert witnesses, dentist Richard Souviron.
Souviron wasn't your typical neighborhood dentist. He fancied himself a pioneer in forensic science, the founding father of a new field of forensics called bite mark analysis, whereby a person could be identified by the marks their teeth leave on the flesh just as they would from the fingerprints left on a crime scene.
When the court asked Souviron about his expert opinion on two puncture marks present on the upper right arm of Julie's body, the dentist didn't blink twice before claiming those were teeth marks and that they were made by Charles. Souviron's deposition convinced the jury which found Charles guilty, sentencing him to life in prison.
Even after 37 years of incarceration, Charles is steadfast that he is innocent and that he is a victim of bad forensics, or just bad science. His lawyer, Chris Fabricant, of course, agrees -- but he isn't any criminal defense lawyer. Fabricant is part of the Innocence Project, a New York-based non-profit that for the last 30 years has helped overturn hundreds of wrongful convictions.
Fabricant recently published a new book, Junk Science and the American Criminal Justice System, in which he goes into detail on how various forensic science techniques that look cool on TV shows like CSI are actually just pseudoscience. These include lie detector tests, blood stain analysis, voice spectrometry (matching a criminal by deconstructing their voices), hair microscopy (the idea that a single strand of hair could be put under the microscope and matched with a suspect's hair), and, yes, bite mark analysis.
Scientists sink their teeth into forensic bite marks
A number of studies have debunked the validity of bite mark analysis since Julie's murder, and a new report released by the National Institute of Standards and Technology (NIST) confirms this after reviewing all the evidence gathered thus far.
The report concludes that “forensic bite mark analysis lacks a sufficient scientific foundation because the three key premises of the field are not supported by the data. First, human anterior dental patterns have not been shown to be unique at the individual level. Second, those patterns are not accurately transferred to human skin consistently. Third, it has not been shown that defining characteristics of those patterns can be accurately analyzed to exclude or not exclude individuals as the source of a bite mark.”
The researchers found no evidence that each individual's set of teeth is unique, despite a prevailing myth that dentition acts like a sort of fingerprint by which a person can be identified. That's not actually true, it seems. Even if teeth were unique to people, bite marks left on the skin can look very different even though they are made by the same person due to distortions caused by the elasticity of the skin, the movement of the victim, or the bite's angle. Swelling and healing can also distort the bite mark by the time evidence is collected.
The worst assumption is that forensic dentistry experts can accurately analyze these patterns. In a 2016 study, experts were shown images of pattern injuries and were first asked if these were bite marks or some other type of injury and, if yes, whether they were made by adults, children, or animals. The experts couldn't seem to agree among themselves whether the injuries were the result of bite marks in the first place, let alone whether they were made by a specific person. Other studies found similar levels of lack of consensus among forensic dentistry experts. In one study where experts were shown pictures of bite marks, in only 8% of cases did the participants agree with high confidence that an injury was caused by a specific human.
“We examined every publicly available, English language scientific article we could find on this topic,” said Kelly Sauerwein, a biological anthropologist at NIST and lead author of the study, adding that they were not able to find any convincing evidence that forensic bite mark analysis actually works as intended.
Although bite mark evidence has never been scientifically validated, many people in the United States have been convicted solely based on sworn testimonies by supposedly expert forensic odontologists. This includes Kennedy Brewer from Mississippi who spent 15 years in prison since 1992, seven of which were spent on death row, for a gruesome crime he never committed. He and Levon Brooks, another man convicted for a similar crime in 1990 using forensic bite mark analysis, were exonerated thanks to the help of the Innocence Project. According to information gathered by the Innocence Project, at least 26 people have been wrongfully convicted based on bite mark analysis. However, some people never got the chance to become exonerated. Such was the case of Eddie Lee Howard, convicted in 1992 of the rape and murder of an 84-year-old Mississippi woman and sentenced to death in 1994 solely based on bite mark forensics.
U.S. courts have not gotten the memo, though. They continue to validate bite mark analysis as genuine forensic evidence because of the longstanding practice of looking back at previous decisions and precedents when deciding how to apply the law. This is a problematic situation because of the way the current court system is set up. Hopefully, forensic bite mark analysis will be out for good at some point in the future. However, people like McCrory may lose many more years behind bars before the law catches up with real science.
This article originally appeared in November 2022.