The Texas Forensic Science Commission recently recommended banning the use of bite mark evidence in criminal cases because of possible mistakes by forensic dentists that could result in wrongful convictions.
It is the first time an agency has officially challenged a forensic technique that’s been used in US courts since the 1890s, despite plenty of criticism over the years. While the Commission only made a recommendation for courts pending further research, Texas could become the first state to prohibit bite mark evidence in criminal proceedings. Other states could soon follow suit.
Rights of the accused advocates praise the agency’s decision as it takes a definitive stand against the infallibility of certain types of evidence. Criminal defense attorney Steve Duckett stated that, “… the Commission made a responsible decision to recommend suspending the use of bite mark evidence in courtrooms until scientific research can better prove its accuracy. As it is now, there’s too much room for subjective interpretation by forensic experts and therefore too much room for error.” He/she added, “Jurors hear the word ‘forensic’ and assume it is foolproof, when in fact, bite mark evidence can be highly refutable.”
The recent moratorium came about because of the Steven Mark Chaney case. In 1987, Chaney was convicted of murdering John and Sally Sweek in Dallas. The main piece of evidence against him was a bite mark on Mr. Sweek’s arm, which a forensic dentist testified was from Chaney.
And despite nine witnesses who swore Chaney was elsewhere when the crime took place, the jurors accepted the expert testimony and convicted him. He spent the next 28 years in prison until a public defender tasked with investigating possible wrongful convictions pursued his case.
As a result, Dallas County prosecutors convinced a judge that no DNA evidence linked Chaney to the crime and the bite mark forensic analysis was simply wrong. They even got the forensic dentist to completely recant his testimony from years earlier, and Chaney was released after spending almost half his life behind bars.
The Chaney case is only one of several high-profile convictions based on bite mark forensics to be thrown out. Hundreds of cases across the country are being reviewed and overturned as experts continue to discredit its validity.
Analysts point to several factors creating doubt. First, human skin isn’t the best medium on which to measure a bite mark. Skin can move and change thereby distorting dental impressions caused by a bite. The possibilities for misinterpretation are significant.
Second, dental profiles can change – teeth can be removed or altered, changing one’s bite configuration over time. Also, and importantly, it has never been scientifically proven that individual dental profiles are unique identifiers. While some studies suggest they may be as distinctive as fingerprints, just as many other studies suggest the opposite.
Even a 2014 study conducted by the American Board of Forensic Odontology (ABFO), the advocacy group responsible for accrediting forensic dentists and setting guidelines, lends skepticism to the assertion that bite mark analysis is certain.
Their report showed that when shown 100 samples, 39 AFBO-certified forensic dental experts strongly disagreed on whether or not an injury was a bite mark at all and whether it had distinguishing, identifiable features that could be used as evidence. Strong disagreement – as in unanimous agreement on only 4% of the samples.
This doesn’t mean that forensic dentistry is useless or meaningless in the justice system. In fact, it is invaluable when identifying human remains or determining a crime victim’s age, health, or socioeconomic status. It can also be extremely helpful in recreating crime scenarios or reenacting physical confrontations. But it certainly isn’t infallible and should not be the primary evidence used to incriminate a defendant.