In our last post, we began a discussion about forensic tests which have recently been debunked as "junk science." These tests have been commonly used to secure convictions in cases alleging serious crimes like rape and murder.
In the courtroom, so-called experts would tout the accuracy and reliability of these tests, which is why test results were often very compelling evidence to juries. But in 2016, the President's Council of Advisors on Science and Technology issued a report stating that several commonly used tests were not reliable or accurate enough to be considered scientifically valid.
Each bite wound is somewhat different, depending on the human or animal doing the biting. Placement of teeth and other characteristics could theoretically create a unique signature that could trace the wound back to the mouth that inflicted it. That was claim behind bite-mark analysis.
Unfortunately, what works in theory does not work in practice. First of all, there is no strong evidence showing that one person's bite marks would leave consistent wounds or patterns. But there is another problem as well: skin is very malleable, and a bite-mark wound changes quickly as the skin stretches or tries to heal itself.
In 1991, a Pennsylvania man named John was convicted of torturing and raping a 55-year-old woman. The woman lived in the apartment building where John had been a maintenance worker.
John had a strong alibi for the night of the crime, and the victim never saw her attacker. Yet John was convicted based largely on bite-mark analysis conducted five months after the crime was committed. In 2009, the Innocence Project was able to exonerate him based on DNA evidence.
In 2016, the American Board of Forensic Odontologists revised their guidelines in such a way that members certified in bite-mark analysis can no longer testify that a given set of bite marks matches a given suspect. The strongest assertion that they can make is that a particular suspect could not be excluded as the potential source of a set of bite marks.
Scientific tests are an important tool for both prosecutors and defense attorneys - but they must actually be scientific in order to be valuable. When junk science is treated as reliable in the courtroom, it quickly leads to a miscarriage of justice.