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Fingerprints, Ballistics & Bite Marks Aren't Indisputable: The Case Against Failed Forensic Science

Eric Gay
Lynn Garcia presents at a Texas Forensic Science Commission meeting to consider recommendations against using bite mark analysis in criminal cases on Feb. 11, 2016, in Austin. The commission ruled bite marks be inadmissable pending further research.

Attorney General Jeff Sessions declined to renew the National Commission on Forensic Science in April, effectively ending federal efforts to standardize how crime scene evidence is interpreted by local law enforcement agencies. It's not because the problems were solved. 

This week on 90.5 WESA’s Criminal Injustice podcast, University of Pittsburgh law professor and host David Harris talks to John Hollway, associate dean and executive director of the Quattrone Center for the Fair Administration of Justice at the University of Pennsylvania Law School.

Hollway says calling forensics a "science" as-is can be misleading.

Their conversation has been edited for length and clarity.

DAVID HARRIS: This all started in 2009 witha landmark report by the National Academy of Sciences saying that forensic science isn't science in the true sense of the word. What does that mean?

JOHN HOLLWAY: A lot of foundational science has been done through large-scale trial and error using clinical trials in a randomized fashion against objective samples. A lot of forensic science is actually more of a subjective comparative discipline where somebody who has made other similar comparisons takes a fingerprint and compares it to a sample, for example. But we don't have that foundational basis of understanding how often that individual might get it wrong. So without the validation of knowing what an error rate is, a physicist or a doctor would tell you maybe that that's not "science," but instead it's simply a subjective comparison.

HARRIS: Even if it's not exactly science, that doesn't mean it's always wrong, does it? Fingerprinting remains the gold standard, and it's usually right, isn't it?

HOLLWAY: Well, we believed it's usually right. That's exactly the challenge, because the fact that out of 100 we get some number wrong doesn't mean that in any individual case we haven't made the right comparison. It simply means that we can't then testify that we are certain that we've got it right or that we know the odds that this fingerprint matches my fingerprint versus somebody else's fingerprint in the population.

HARRIS: Fingerprinting, ballistics, bite mark comparisons [and] other methods of investigations are sometimes portrayed in court by prosecutors or forensic experts and others as being foolproof. "It's a match. We're 100 percent certain." Vocabulary like that. But that isn't the way true science works is it?

HOLLWAY: It isn't. Every test has an error rate. There is no perfection in the universe. And so without knowing what the error rate is, without knowing what the incidence of something in the population is we can't actually convey in any honest way what the likelihood that our comparison is accurate is. All we can really say is, "I believe this is a match."

HARRIS: The National Commission on Forensic Science was making a real effort to make that fallibility of expert testimony more clear was that working?

HOLLWAY: Well what the commission had accomplished in its first four years, most substantially, was making sure that the U.S. Department of Justice was only working with accredited crime labs. It had established a national code of professional responsibility. It had made recommendations about the procedures and steps labs should take when they discovered an error had occurred, and all of that is very important foundational work to improve the level of quality across the forensic disciplines. We were really starting to engage on some of these issues around the translation of science into legal testimony and making sure that we were making recommendations about how to improve the validation and the scientific rigor around some of these comparative disciplines. But we really hadn't gotten to that at the time the Department of Justice elected not to renew the commission's charter.

HARRIS: Are there going to be more wrongful convictions in the future because of that?

HOLLWAY: As long as we are using forensic testimony in the way we are currently using it today, we run the risk that there will be more wrongful convictions in the future just as there have been in the past. Einstein's definition of insanity is doing the same thing again and again and expecting a different result. If we don't improve these disciplines, if we don't help law enforcement officers get it right more often, we're going to continue to have errors and not know that they're happening. And so we need to get back into this arena and continue to engage to improve it as quickly as possible. 

Criminal Injustice is recorded at the studios of 90.5 WESA. Find more at