However, an investigation currently underway in Travis and Williamson counties in Texas has raised concerns about the way examiners have been analyzing DNA evidence in hundreds of criminal cases.
Recently, Travis County District Attorney Rosemary Lehmberg highlighted an apparent issue with the database it uses to work out DNA statistics, which are used in court proceedings as probabilities that a given sample included the DNA of a certain person, reported by Statesman.
Lehmberg said in the report her office is not sure how many Travis County cases are affected but says it is working to find out and to notify the parties involved. The findings are alarming because they may affect numerous criminal cases.
“The potential impact of changes to the mixture protocols and the database is still unknown, but they may have a material impact on some criminal cases,” Lehmberg said in the report.
She expects a large scale investigation to be held that requires additional attorneys and paralegals being added to Conviction Integrity Unit. “In the interim, this office will work to facilitate any requests for DNA reviews based on the changes,” she added.
Earlier this year, the FBI notified crime labs across the country that investigators discovered laboratories were using outdate protocols to interpret DNA results,
‘The issue meant some prosecutors had been overstating the reliability of DNA evidence in court, which is often presented as accurate to within a fraction of a fraction of a percent in cases.
The Washington Post reported the FBI notified crime labs across the nation that it found errors in data “used by forensic scientists in thousands of cases to calculate the chances that DNA found at a crime scene matches a particular person.”
The bureau traced these errors extended back as far as 1999. The FBI said these errors were unlikely to lead to dramatic changes that would affect the outcomes of cases. It submitted the research findings to support that conclusion in the July issue of the Journal of Forensic Sciences.
Defense attorneys and crime labs have been more skeptical, saying they want to find out more about the problem before conceding it would not make much difference in any given case.
The experience in Texas suggests the FBI may have understated the potential effect of the problem.
The issue blew up when district attorneys started requesting Texas Department of Public Safety forensic labs to retest evidence for use in upcoming trials. Galveston County District Attorney Jack Roady requested DNA samples be reassessed in a murder case and discovered a dramatic change in the likelihood that the DNA was unique to an individual.
Originally the DNA found a one to a million match to a defendant, meaning investigators would have to go through a million people before finding a similar match. This seemed to be powerful evidence that the prosecutors had their man. However, using the new protocol the likelihood of a match was one in 30 or 40, meaning there was a high probability that someone else could have been the killer.
The Texas Forensic Science Commission, which sets out standards for physical evidence in state courts, and the Texas District and County Attorney’s Association are working closely with the two Texas counties on addressing the issues. The Department of Public Safety sent a letter Sept. 10 notifying state officials of the changes.
Williamson County District Attorney Jana Duty has said she discovered the changes in DNA mixed sampling in September. Her office reports that since 1999, it has 955 mixed DNA samples associated with cases that are impacted by the new interpretation of the DNA tests. It’s a significant number.
The issues in Travis and Williamson counties raise larger concerns about how widespread this problem is in Texas and beyond and how many defendants have been wrongly imprisoned due to suspect DNA protocols.