DNA is supposed to be the gold standard of evidence. Supposedly so distinct it would be impossible to convict the wrong person, yet DNA evidence has been given far more credit than it’s earned.
Part of the problem is that it’s indecipherable to laypeople. That has allowed crime lab technicians to testify to a level of certainty that’s not backed by the data. Another, much larger problem is the testing itself. It searches for DNA matches in samples covered with unrelated DNA. Contamination is all but assured. In one stunning example of DNA testing’s flaws, European law enforcement spent years chasing a nonexistent serial killer whose DNA was scattered across several crime scenes before coming to the realization the DNA officers kept finding belonged to the person packaging the testing swabs used by investigators.
The reputation of DNA testing remains mostly untainted, rose-tinted by the mental imagery of white-coated techs working in spotless labs to deliver justice, surrounded by all sorts of science stuff and high-powered computers. In reality, testing methods vary greatly from crime lab to crime lab, as do the standards for declaring a match. People lose their freedom thanks to inexact science and careless handling of samples. And it happens far more frequently than anyone involved in crime lab testing would like you to believe.
An op-ed about the failures of crime lab DNA testing at the New York Times — written by Boise State Professor of Biology Greg Hampikian — discusses this ongoing problem using some science of his own: a recently-released NIST study. (h/t Grits for Breakfast)
Researchers from the National Institute of Standards and Technology gave the same DNA mixture to about 105 American crime laboratories and three Canadian labs and asked them to compare it with DNA from three suspects from a mock bank robbery.
The first two suspects’ DNA was part of the mixture, and most labs correctly matched their DNA to the evidence. However, 74 labs wrongly said the sample included DNA evidence from the third suspect, an “innocent person” who should have been cleared of the hypothetical felony.
This is already a problem. People’s lives are literally on the line and crime lab testing is more likely to make the wrong call on evidence than the correct one. What’s truly disturbing is this study was completed in 2014, but the report was apparently buried by the scientists it implicated. As Dr. Hampikian states in his op-ed, the study’s results may still be unpublished if it weren’t for forensic scientists publicly complaining about the burial.
Four years have passed since the study’s completion and it appears no improvements have been made. The study notes testing protocols vary widely and very little effort is being made to improve error-prone procedures. In addition, the study [PDF] comes with a disclaimer meant to dissuade litigants from challenging DNA evidence by quoting the study’s findings.
The results described in this article provide only a brief snapshot of DNA mixture interpretation as practiced by participating laboratories in 2005 and 2013. Any overall performance assessment is limited to participating laboratories addressing specific questions with provided data based on their knowledge at the time. Given the adversarial nature of the legal system, and the possibility that some might attempt to misuse this article in legal arguments, we wish to emphasize that variation observed in DNA mixture interpretation cannot support any broad claims about “poor performance” across all laboratories involving all DNA mixtures examined in the past.
This certainly doesn’t raise the reader’s confidence in crime lab DNA testing. Instead, it gives the impression the four-year delay between completion and public release was for wagon-circling purposes as crime lab forensic scientists looked for ways to mute the impact of the study’s findings.
But there are also problems with the study itself. The authors of the study appear far too willing to cut crime labs slack for their failures. Rather than point out the problems originating from a lack of standardized processes, the study uses them to excuse the failures, as if unintentionally nailing the wrong person for the crime was somehow worthy of gold stars for effort. Here’s Hampikian’s take:
It is uncomfortable to read the study’s authors praising labs for their careful work when they get things right, but offering sophomoric excuses for them when they get things wrong. Scientists in crime labs need clear feedback to change entrenched, error-prone methods, and they should be strongly encouraged to re-examine old cases where such methods were used.
The study confirms much of what has been exposed earlier: DNA evidence may be based on hard science, but any small variable — including the inevitable tainting of DNA samples — has the ability to throw things off. And when it’s used as evidence in criminal trials, it has the potential to destroy lives. This study shows — at least indirectly — the labs handling DNA evidence aren’t taking it nearly as seriously as they should.