Questioning the Use of DNA Testing Software in Criminal Prosecution

Questioning the Use of DNA Testing Software in Criminal Prosecution

The use of DNA evidence in criminal trials has become ubiquitous. Because DNA evidence is highly persuasive to judges and juries, several new tests purport to make positive DNA matches using minuscule amounts of matter or even matter that has been polluted. As defense attorneys push back on these new methods, they are running into a brick wall: The companies that create these tests and the forensic labs that use them refuse to turn over the source code for defense analysis.

In California, the Electronic Frontier Foundation (“EFF”) recently filed an amicus brief arguing that courts should require the government to turn over the source code of any software used for DNA analysis. In the case at issue, the government used a DNA matching software program called TrueAllele to produce a DNA match. The defendant requested the TrueAllele source code but was denied.

The EFF argued that both due process and the rules of evidence require handing over the code. Without it, the defendant is unable to examine how the software works and is thus unable to mount a proper challenge to the results. EFF staff attorney Stephanie Lacambra said that a defendant’s right to a fair trial in a criminal prosecution is paramount.

“Errors and bugs in DNA matching software are a known problem,” said Lacambra in a press release. “At least two other programs have been found to have serious errors that could lead to false convictions. Additionally, different products used by different police departments can provide drastically different results. If you want to make sure the right person is imprisoned—and not running free while someone innocent is convicted—we can’t have software programs’ source code hidden away from stringent examination.”

The two other programs referred to by Lacambra are the “high sensitivity testing” of trace DNA amounts and the Forensic Statistical Tool (“FST”), both of which were heavily used in New York City and have since been abandoned. In a September 4, 2017 article, The New York Times detailed the rise and fall of these programs. Just like TrueAllele, defense attorneys routinely requested, and were denied, source code. When a judge was finally persuaded to allow review of the FST software, the computer scientist who examined the code said, “The correctness of the behavior of the FST software should be seriously questioned.” The city’s DNA lab replaced both programs soon after the analysis.

EFF staff attorney Kit Walsh summed up the importance of disclosing DNA software source code to the defense. “Software errors are extremely common across all kinds of products,” said Walsh. “We can’t have someone’s legal fate determined by a black box, with no opportunity to see if it’s working correctly.”


Originally published in Criminal Legal News on February 16, 2018.