In October 2022, the National Institute of Standards and Technology (NIST) released a draft report that shocked some people in the criminal justice system. The report was a response to the landmark 2009 study by the National Academies of Sciences, Engineering and Medicine that called into question whether a variety forensic science techniques are scientifically valid.
The NIST reviewed all of the available English-language scientific literature about bite mark analysis because it was one of the techniques the 2009 study had found lacked much scientific foundation.
What it found was that bite mark analysis indeed lacks a clear scientific basis. The group identified three basic assumptions about bite mark analysis that have never been scientifically proven.
Those assumptions are 1) that bite marks are unique to one individual; 2) that bite marks on skin are accurate representations of the biter’s teeth; and 3) that experts can reliably match bite marks to a specific person’s mouth or dental records. It turns out those assumptions are questionable at best.
The science just isn’t there – or it is and it undermines bite mark evidence
First of all, there is no scientific evidence demonstrating that human bite patterns are actually unique to each individual. Surprisingly, no studies have ever been done to show this. No studies have been done to show how common or uncommon certain distinguishing features are.
Second, there is some evidence showing that bite marks may not get transferred accurately to human skin when someone is bitten. Human skin is elastic and not a good medium to accept marks. This elasticity, along with any movement by the victim, could skew the bite mark. So could swelling and healing. These distortions mean that bite marks don’t accurately reflect the teeth of the biter.
Third and finally, the NIST report found that experts in bite mark analysis disagreed with each other when presented the same images of bite mark injuries in a scientific study. In some cases, they even disagreed about whether the injuries in the images were bite marks.
When the experts did agree that the images contained bite marks, they didn’t agree most of the time on whether the marks were human or animal in origin or made by adults or children.
In other words, there was no evidence experts could reliably match any image of a bite mark to a particular individual. And, there is pretty good evidence that they could not do so.
That’s not good enough to use as evidence in court.
Nevertheless, prosecutors around the nation continue to offer bite mark evidence in criminal cases. Even after several authoritative groups like the NIST have debunked bite mark analysis, many people are still behind bars based on this evidence.
When someone’s freedom is at stake, the evidence brought by the government needs to be unimpeachable. A fair system demands it.