In 2009, a committee of the prestigious National Research Council (NRC) published a report for Congress that shocked the entire criminal justice system. Congress had asked the NRC to evaluate the scientific underpinnings of commonly used forensic evidence and suggest if any improvements needed to be made.
The NRC concluded that most forensic evidence, including virtually all types of pattern-matching evidence, is not backed by science at all. No scientific basis exists for the proposition that patterns from one source can be accurately matched to other sources.
That leaves a wide range of forensic techniques without any research to back them up, such as:
- Tool mark comparison
- Bite mark comparison
- Hair comparison
- Tire and footwear impressions
- Bloodstain pattern analysis
- Handwriting analysis
According to a new book by the head of the strategic litigation division of the Innocence Project, there is good reason to conclude that these techniques also don’t yield good evidence. It’s not just that the techniques are unproven; it’s that they’re inaccurate.
In the book “Junk Science and the American Criminal Justice System,” Chris Fabricant notes that these forensic techniques have been heavily implicated in numerous wrongful convictions.
Bite mark comparison is a relatively straightforward example of a junk science, he says. There is simply no scientific reason to believe any of the underlying assumptions of this technique, which are:
- That dentition is as unique as DNA
- That skin is capable of taking accurate impressions of bite marks
- That forensic dentists are able to match bites on skin to a particular person’s mouth
It’s more than just unproven, however. Inaccurate bite mark comparisons have been the source of over 35 wrongful convictions and indictments, including that of Wisconsin’s Robert Lee Stinson, who was exonerated in 2009 after spending 20 years in prison.
Why do courts allow discredited pattern-matching evidence?
According to Fabricant, there are numerous factors at play. One is simply the differing world views between the law and science.
In science, hypotheses are tested and then accepted if proven or rejected if unproven. Then, new hypotheses are considered and tested. It’s a search for truth that depends on new evidence often demonstrating a new understanding of reality.
The law is more concerned with stability and ensuring that each person gets the same legal result across many courts. It relies on precedent, not innovation. You might say the law actually resists innovation.
Unfortunately, there is a stubborn series of legal precedents that say pattern-matching techniques aren’t actually scientific but mere comparison, which anyone can do. Therefore, the precedents conclude, pattern-matching techniques don’t need to be backed up by science at all.
The fight against junk science in the courts continues. At stake is the freedom of innocent people.