The criminal justice system has a problem. No one knows just how reliable some types of forensic evidence are. These forensic fields were developed by crime investigators instead of by scientists. Not only haven’t they been proven to be reliable, there’s a question of whether or not they’re based on science at all. Some of them are better classified as superstition, but the criminal justice system has been slow to weed them out.

Bad forensic evidence usually makes its way into Utah courtrooms through expert testimony. Someone can testify about their credentials—frequently from spurious colleges or organizations—and then the court certifies them as an expert in a particular field. Under the Utah Rules of Evidence, judges are supposed to prevent experts from testifying about junk science. Utah Rule 702 governs expert testimony, and judges are required to make sure that the specialized knowledge that the expert purports to have is “reliable,” “based upon sufficient facts or data,” and has been “reliably applied to the facts.” Most judges do not have the expertise necessary, however, to determine if an expert’s testimony actually meets that criteria.

In a previous post, I argued that juries demanding that forensic evidence accompany eyewitness testimony has been a positive trend for criminal justice. I still believe that, but it’s also important that hard science support all forensic testimony.

The best forensics were developed independently from crime investigation and have other applications. DNA evidence is the gold standard for good forensic evidence. Everyone has DNA, it’s unique (even identical twins have a little variation), it’s quantifiable, and DNA tests can be replicated from one lab to another. Through CODIS (the Combined DNA Index System), the FBI keeps a large database of individuals’ DNA to help identify suspects in certain crimes. The one drawback is, unlike on television where it takes just a few minutes, it actually takes weeks to get the results.

Some forensic fields lack applications beyond crime investigation and don’t have independent verification. Those fields need to be subjected to the scientific process. That includes independent experimentation, peer review, and the ability to replicate conclusions. Most people are surprised when they learn that much of the forensic evidence that we were led to believe is scientific, has actually never been subjected to the scientific process, and no one has proved that they are reliable. In such fields, two different experts can come to completely different conclusions or their conclusions can be influenced by what they know about the crime they are investigating.