If a computer DNA matching program gives test results that implicate you in a crime, how do you know that the match is correct and not the result of a software bug? The Electronic Frontier Foundation (EFF) has urged a California appeals court to allow criminal defendants to review and evaluate the source code of forensic software programs used by the prosecution, in order to ensure that none of the wrong people end up behind bars, or worse, on death row.

In this case, a defendant was linked to a series of rapes by a DNA matching software program called TrueAllele. The defendant wants to examine how TrueAllele takes in a DNA sample and analyzes potential matches, as part of his challenge to the prosecution’s evidence. However, prosecutors and the manufacturers of TrueAllele’s software argue that the source code is a trade secret, and therefore should not be disclosed to anyone.

“Errors and bugs in DNA matching software are a known problem,” said EFF Staff Attorney Stephanie Lacambra. “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 public has an overriding interest in ensuring the fair administration of justice, which favors public disclosure of evidence. However, in certain cases where public disclosure could be too financially damaging, the court could use a simple protective order so that only the defendant’s attorneys and experts are able to review the code. But even this level of secrecy should be the exception and not the rule.

“Software errors are extremely common across all kinds of products,” said EFF Staff Attorney Kit Walsh. “We can’t have someone’s legal fate determined by a black box, with no opportunity to see if it’s working correctly.”

For the full brief in California v. Johnson: