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Opinion The latest from the world of bite mark evidence

There have been some new developments and stories regarding the dubious forensic specialty of bite mark matching.

The first story comes from Minnesota, where a judge has decided to allow bite mark analysis in the murder trial of a man accused of killing his infant daughter. The Grand Rapids (Minn.) Herald-Review reports that Judge Korey Wahwassuck ruled that “testimony about bite mark evidence would be allowed, but she clarified that testimony stating that a particular person made the bite mark would not be allowed.”

I presume this means that while a bite mark analyst won’t be permitted to say that the defendant definitively made the mark, he or she would be able to say that the defendant is “included” or can’t be excluded as the biter. The problem is that there’s no real science behind these conclusions, either. There’s no evidence that human dentition is unique in this way. Nor is there any evidence that human skin registers and preserves marks made by teeth in a useful way. Except for a few extremely rare scenarios (a suspect doesn’t have any teeth, for example), “inclusion” and “exclusion” mean very little. While it may be technically true for a witness to say “I can’t exclude the defendant” as the source of a bite mark, it would also be true to say that of everyone else in the courtroom with a full set of teeth.

The added problem here is that there’s research suggesting that when they evaluate forensic testimony, jurors tend to think in binary terms. Either the testimony implicates the suspect, or it doesn’t. For example, this study of fingerprint evidence by Brandon Garrett and Gregory Mitchell, for example, found that “the particular phrase chosen to describe the finding of a match—whether simple and imprecise or detailed and claiming near certainty—had little effect on participants’ judgments about the guilt of a suspect.” In other words, to many jurors’ ears, “I can’t exclude the defendant” sounds about the same as, “the defendant did it.”

Finding the right way to state probabilities to juries is a difficult problem. But it’s only a problem that needs to be addressed in those forensic fields that are supported by scientific research. The little scientific research that has been done on bite mark analysis so far has cast doubt on the field’s core assumptions. So it would be best to just exclude it altogether. Judge Wahwassuck apparently doesn’t see it that way. Unfortunately, thus far, neither has any other judge in the country who has been asked to rule on the question directly.

The second story comes from Ohio, where former Akron police captain Douglas Prade is seeking to overturn his conviction for murdering his ex-wife in 1997. Margo Prade, a doctor, was found dead in her van in a parking lot. She had been shot six times with a handgun and had struggled with her killer.

While there was evidence that the Prades had a contentious relationship, the only physical evidence linking Douglas to his wife’s murder scene was testimony from a bite mark analyst, who claimed that marks found on Margo Prade, allegedly made through her lab coat, could only have been made by Douglas’s lower teeth. Another bite mark analyst said the marks were “consistent with” Prade’s teeth. Three jurors later said in interviews that the bite mark evidence was critical to their vote to convict.

DNA testing done at the time was too primitive to be of much use. But in 2012, DNA taken from blood and saliva on Margo Prade’s lab coat and scrapings from her fingernails did not match the DNA of her ex-husband. Citing the results of those tests, an Ohio judge threw out Prade’s conviction and ordered Prade released. But that judge’s decision was then overturned by an Ohio appeals court, which was concerned that the DNA tests revealed profiles of between two and five men. None of those men were Prade, but the court was too troubled by the possibility that the DNA samples had been contaminated to give the tests much weight. Prade was ordered back to prison.

Now, more advanced DNA testing on saliva around the bite mark has again excluded Prade. And this time, the tests found only the profile of one other man.

According to the Akron Beacon Journal, the same prosecutors who once argued that the person who bit Margo Prade is also the person who killed her are now arguing that just because the saliva found around the bite wasn’t Douglas Prade’s doesn’t mean he isn’t the person who killed his ex-wife. They’re basically asking the judge to rely on bite mark analysis that even the American Board of Forensic Odontology now says was unsound while, at the same time, asking the court to disregard DNA tests on saliva found at the site of the bite that exclude Prade as the source. It’s an astonishingly cynical argument.

The final bite mark story comes from Louisiana, where defense attorneys are invoking bite mark analysis in attempt to vindicate their client. DNA testing has apparently implicated a man named Joenell Rubin in a 27-year-old murder that had gone cold. But Rubin’s defense team found an old letter from a forensic specialist claiming that bite marks found on the victim were administered by someone other than Rubin.

So here we have defense attorneys doing what prosecutors are doing in Ohio — asking a court to embrace bite mark evidence even in the face of DNA evidence (although in the form of a very old letter that can’t be cross examined). On the one hand, if prosecutors are going to continue to use bite mark testimony, it doesn’t make much sense to ask defense attorneys to unilaterally disarm. On the other hand, it’s hard to see how a defense attorney could ethically submit evidence he or she knows is fraudulent. I obviously have no idea if the defense attorneys in this case honestly believe that bite mark analysis is scientifically valid. But they shouldn’t get any more deference than prosecutors. This case also is by no means the first time defense attorneys have tried to rely on bite mark analysis.

In some ways, it seems worse when prosecutors deploy transparently bogus evidence because their obligation is to seek justice, not to win convictions at any cost. A defense attorney’s job is to vigorously defend his or her client, within a few basic ethical boundaries.

The real problem is that we’ve entrusted judges to be the gatekeepers of science in the courtroom, and they’ve fulfilled that function about as well as you might expect from people trained in law, not science — pretty poorly. This sort of evidence ought to be rejected no matter which side is trying to introduce it.

To that end, here’s one more story, from the Boston Globe. It isn’t about bite mark evidence, but about another pattern-matching field of forensics. And it’s better news.

George Perrot could soon be free at last. He should never have been behind bars.
In a groundbreaking ruling with national implications, a Superior Court judge on Tuesday ordered that he be given a new trial on the rape charge that put him behind bars for so long. It is the first time a judge in the United States has ruled that justice was denied because prosecutors relied on forensic hair analysis, now widely discredited.
Perrot was charged with raping an elderly Springfield woman in 1985, when he was 17, even though the victim, a neighbor, insisted he was not her attacker.
No matter, prosecutors argued: There was other evidence against Perrot — most notably, a single strand of hair found at the scene. On the stand, an expert witness from the FBI testified that the hair, found on the victim’s bed, was a match for Perrot, and that only someone “with a lesser amount of training” would conclude otherwise. In closing arguments, prosecutor Francis Bloom told jurors the hair evidence was so strong that Perrot could be innocent only if police had planted that strand in the victim’s house.
The jury convicted him.
We now know that Bloom crossed a line — in this and in other ways — presenting the jury with a false choice, a fact underscored by Judge Robert J. Kane’s thoughtful and thorough decision Tuesday.

Kane dismissed Perrot’s conviction, noting that hair fiber analysis as it was presented at Perrot’s trial has been widely discredited, including by the FBI, which pioneered the field. As Globe columnist Yvonne Abraham points out, the ruling runs counter to a century of precedent and if upheld (as it should be) would send shock waves through the forensic science community. But Kane wrote, “It is not a close call.”

There were other problems with the case, including a host of prosecutorial misconduct. But the main piece of evidence against Perrot was the hair fiber analysis. With that gone, the case against him fell apart. If other judges follow Kane’s lead, other forensic fields long accepted by the courts may start to fall apart, too.