Bite Mark Evidence Still Getting It Wrong

Bite Mark Evidence Is Still Getting It Wrong – But Courts Are Fine with That

Bite mark evidence impressed many in the 1970s and 1980s. As an early example, bite marks received plenty of attention during the trial of Ted Bundy. Prosecutors fell in love with the idea that a positive and reliable match between dental records and physical evidence on a victim’s body could be the key to  getting their conviction. Many of them still readily accept that the evidence is infallible, and that each and every time they rely on this shaky evidence they are getting another dangerous biter off the streets. Crime shows like CSI and Forensic Files have joined law enforcement and prosecutors in this overly eager acceptance, claiming a “positive match” simply solves the case. As a result, jurors can also readily accept statements from so-called experts that this mark or that mark positively identifies a unique dental pattern. Because of this, courts have a duty to intervene and reduce the risk of the presentation of evidence that has been shown to be unreliable and incorrect. Failure to do so leads to wrongful convictions, and all of us have a part to play in preventing those.

Why Not Just Leave It to the Jury?

As a juror, why would you doubt what the doctor on the witness stand is telling you? The court presents a witness to you as an expert. Unlike other witnesses, they are allowed to share their expert opinions because the court has accepted that the witness is an expert. The witness has a fancy title like forensic odontologist that seems to just exude credibility. Maybe he or she is certified by a board and you hear that this person has testified about bite mark evidence in other trials. Then that person tells you that the mark on the victim definitely lines up to the Defendant’s teeth. They talk about the overall pattern of the teeth, and “unique” features like wear patterns, dental work, and slight differences in tooth spacing and orientation. Maybe the witness will show you an overlay, and it looks like a match to you too. What are you, as a juror, to do with that? It is persuasive to the typical juror who must rely upon the expert when that expert says something like “This five tooth pattern could only match one person in over a million.”  Or when they say they are certain the pattern matches the Defendant’s teeth and no one else’s. At any point in all this, do you suspect the judge is expecting you to truly weigh the scientific reliability or methods behind these conclusions? Do you suspect the judge has told attorneys who fought over the reliability of the science involved that it’s up to the jury to evaluate that, instead of the court? How would you?

What’s the Problem?

The huge, glaring, major, not-to-be-overlooked reality check comes when it turns out that the forensic odontologist the jurors relied on and the court presented as an expert was flat wrong. It was not even a bite mark, but the work of insects or crawfish. Those marks were not even made by human teeth. The “expert” was not using objective scientific principles to reach that conclusion. Interestingly, the board that certified that witness requires him to testify first before he can be certified. So he must to try to convince a jury before he’s even certified by this board who is supposed to regulate these experts. As a juror, you might never hear that the board has never, ever, decertified anyone. Even the experts who have been proven wrong. Even one of the best known experts who no longer believes in the science and no longer does bite mark analysis, who stepped down after learning that his testimony convicted innocent people, was not decertified. He eventually made his own decision to leave the board. The expert witness with the fancy title almost certainly believed what he was saying at the time, and years later he might take it all back. He could say “I thought I was right, but the science turned out to be junk”. Of course, these are not simply made up facts.  All this has happened in bite mark cases. Are you, as a juror not knowing any of this, able to sort that in the context of a murder trial and in real time? Is it in any way fair or reasonable for a court to expect you to? Of course not. But it is happening. Often. And bite mark evidence is sending innocent people to prison. Experts who testified with certainty are changing their minds, doubting their outcomes, or getting out of the field completely.  But the people they sent to prison on false evidence can remain in prison anyway.


Stories in crime shows like CSI and their portrayal that bite mark evidence is hard and reliable science are not real. But the scenario I described above is based on true events, from the expert who is absolutely certain but wrong, right down to the crawfish. We know for sure that over 24 people have been wrongfully charged or convicted based on bite mark evidence that turned out to be completely wrong. Those are just the ones we are sure about, and that is only since 2000. Before any of those occurred, a study conducted in 1999 showed that attempts to match dental records and tooth impressions to so-called bite mark evidence turned out to be wrong 63% of the time. In other words, courts are relying on evidence that has been shown to be wrong more often than it is right. After that study, courts and law enforcement have continued to rely on this evidence, resulting in wrongful arrests and convictions based on misidentifications.

Bite mark evidence gained its momentum based on unsubstantiated assumptions from decades ago, and modern testing and studies have consistently undermined its credibility as a means of matching.  When held to transparent scientific standards, the assumptions that support any sort of reliance on matching bite marks (as opposed to eliminating suspects using bite marks) have fallen away in the face of facts. Improvements in DNA technology have only increased doubts about the reliability of bite mark evidence, as many people convicted based upon the confident testimony of forensic odontologists have now also been proven not guilty through DNA testing.

Bite mark analysis as evidence of a match between the mark and a defendant’s teeth depends upon a collection of assumptions that have not been borne out by scientific testing and study. Two of these primary assumptions were noted in a White House briefing on the subject just last year. First, is the assumption or assertion that there are significant and meaningful differences in dental characteristics between all, or at least most, people. This sounds true enough. It is one of those statements that many people (jurors, judges, and even attorneys) may just accept because it sounds like it is probably true.  There just are, right? It makes us think of similar assumptions we have about fingerprints. In fact, in their evidence collection guide, the Colorado Bureau of Investigations (CBI) goes so far as to assert that bite mark evidence can be as important as fingerprint evidence. Bite mark evidence has been compared to fingerprint evidence by experts in testimony in the past, and if you haven’t guessed already, the public has been repeatedly invited to that comparison by T.V. shows like CSI. One does not have to look far to find that comparison. But are our dental impressions truly that unique? It appears for experts willing to testify as to their scientific certainty of a match, this was just an assumption that repeatedly sent innocent people to prison. Many stated, as offered in the example above, that a given five-tooth impression match could only occur one time in more than a million comparisons. However, when actual science got involved in 2010, a study of 344 impressions found 32 five-tooth matches.

Another assumption pointed out in the White House briefing to the President regarding forensic evidence, is that the bite mark evidence assumes the mark itself reliably captured distinguishing characteristics. In criminal cases involving bite marks, the prosecution is trying to get the jury to believe that human skin accurately captured unique features in a bite mark. There are too many assumptions in there to break apart in a blog post. But suffice it to say that studies have shown, and the White House briefing relays, that that is bogus. Human skin, especially, stretches, compresses, twists, reacts differently to different amounts of pressure from different directions, bruises differently, and heals differently from person to person. To say it is unreliable is an understatement. In fact, many so-called forensic experts, when not briefed in advance regarding what the police want to hear from them, are unable to even agree on whether a given mark is in fact a human bite mark.

But Bite Mark Evidence Has Exonerated Innocent People Too…

Simply put, it is a far more reliable statement that a given mark does not match the dental impressions of these 300 people than to say that it does match this one specific person. Despite this widely acknowledged reality, the vast majority of bite mark evidence introduced in criminal courts is introduced by prosecutors. However, for the evidence to be useful to the prosecution it needs to match a specific person rather than eliminate a group of people. So a match has to be extremely rare to be useful. That is a problem for the prosecution, as the studies simply do not show that. Again, consider the study of 344 impressions resulting in 32 matches. Determining that a bite mark does not match, often based upon significant differences, is a far simpler and much more reliable process than attempting to positively match unique identifiers that have been shown to not actually be unique at all.   Bite mark analysis mainly fails in the attempt to positively match, and where bite mark evidence has been used by the defense, it has mostly been for the purpose of reversing the damage of a misidentification put forward by the prosecution.

Who Cares?

Bite mark evidence is not just something that criminal defense attorneys are challenging. This is an issue that has had plenty of attention from various credible sources.  Over the past ten years, articles have appeared in credible news outlets like The New York Times, The Washington Post, USAToday, BBC News, and the Denver Post, questioning the validity and continued use of bite mark evidence in courts. Recently, Last Week Tonight host John Oliver highlighted this issue and questioned the reliability and continued use of bite mark evidence in courts. Most of the background information gathered for this blog post was collected from those sources and the government funded study and briefing by the President’s Council of Advisors on Science and Technology. These sources tend to show that, at least with regard to bite mark evidence as a tool for attempting a match, this is not an issue of interest only to a limited group of defense attorneys. This is an issue of concern to a growing number of scientists and regular citizens who do not want unreliable science in our courtrooms.

Texas, where some believe the use of bite mark evidence in courts found its footing, has seen organized pushback on this issue. The Texas Forensic Science Commission recommends against using bite mark evidence to show a match in court.

Why Are Courts Still Using It?

Courts often decide whether evidence is admissible based on whether it has been used in court before.  As mentioned above, Last Week Tonight with John Oliver covered this recently, and that show implied that this evidence is routinely being approved for presentation to juries simply because it has been before. In Colorado, the law requires the courts to consider – especially when challenged by the defense to do so – the validity of the scientific methods and processes used by an expert when determining whether expert or scientific evidence is admissible. However, use of this evidence has built up momentum with courts that is disproportionate to its actual usefulness. At least one article reviewed while researching this post claimed that no court anywhere had been known to reject the admissibility of bite mark evidence. While we are unable to independently verify that claim, there is evidence that bite mark evidence still has not been successfully challenged in court. A closely monitored case in another state received national attention earlier this year when it took up this issue and that court again allowed the evidence to be presented to a jury. Interestingly, the first known case of bite mark evidence being used in a Texas court in the 1960s justified allowing presentation of the evidence based upon bite mark evidence being used once before in the 1950s.

Another common argument, and another justification for allowing the evidence to be admitted despite all these doubts about its usefulness, is that it is up to the jury to decide what is true and what is not.  But looking back to the beginning of this post, and imagining oneself in the role of juror, a person can see how much of an ineffectual punt of the issue that really is. Jurors in trial are not in a good position to weigh the veracity of a scientific method or scientific reliability of evidence that is as widely questioned and doubted to the extent bite mark evidence is. That duty better fit for the judge, and judges should hold this evidence to an objective scientific standard. It must be limited to its reliable uses, which do not include matches to a specific person. No use of evidence shown to be so consistently unreliable, and to have resulted in decades of wrongful convictions, should be presented to juries.  Courts and judges have done this before in the case of polygraph examinations. They can and should do so again with bite mark evidence when used to prove a unique match to a specific person.

About the Author:

Vernon Ready is a trial lawyer serving the Denver metropolitan area. The firm, Ready Law, represents injured clients who are victims of negligence as well as those seeking help with divorces and child custody disputes.

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