Crime dramas depend on impressive forensic evidence to prove who did it by the end of an episode. Real life is not so neat. Can past valid forensic analysis or methods be discredited? Yes, forensic science is actually second only to eyewitness errors on the list of evidence that contributes to wrongful convictions.
For example, a 2001 murder conviction included damning evidence from a forensic dentist about a bite mark. The testimony rejected the possibility of error with this statement, “I believe that with reasonable medical certainty without any reservation that these makes were created by [defendant’s] teeth.”
Fast forward almost 20 years and bite-mark analysis has largely been discredited. The defendant in the case served 18 years while waiting, but DNA evidence exculpated him and the expert recanted.
This bite-mark technique relied on two premises (neither ever proved):
- Human dentition/bite is unique like DNA
- Skin can precisely record a dental impression that could be accurately matched
A journal article in 2016 reported on the lack of empirical evidence to support the claims of forensic dentists.
This niche of forensic science was singled out this as “particularly dubious” in 2009 by a National Academy of Science publication. A President’s Council of Advisors on Science and Technology report in 2016 put the odds of turning this type of analysis into a scientifically valid method at nil.
In Texas, a state Commission on Forensic Science placed a “moratorium” on this type of evidence.
Other forensic evidence laid to rest
Bite-mark evidence is not the only evidence that has not stood up to scrutiny. Comparative bullet lead analysis and microscopic hair analysis (a FBI review of cases found scientifically invalid testimony in 95 percent of cases) have met a similar fate.
How do we protect the rights of those accused of crimes as the reliability of forensic methods change over time? A stricter limit on the admissibility of expert forensic opinions is one way. Providing error rates for various recognized forensic methods is another. It is too easy for experts to overstate the probative value of evidence.
While courts cannot foresee how science will change, they could prevent experts from using the language “to a reasonable degree of scientific certainty.” This was a recommendation in the 2016 President’s Council report.
A tough criminal defense attorney is the other check to protect your rights in the system.