If you’re accused of a crime, you have a right to examine and challenge the evidence used against you. In an important victory, an appeals court in New Jersey agreed with EFF and the ACLU of NJ that a defendant is entitled to see the source code of software that’s used to generate evidence against them.

The case of New Jersey v. Pickett involves complex DNA analysis using TrueAllele software. The software analyzed a DNA sample obtained by swabbing a weapon, a sample that likely contained the DNA of multiple people. It then asserted that it was likely that the defendant, Corey Pickett, had contributed DNA to that sample, implicating him in the crime.

But when the defense team wanted to analyze how that software arrived at that conclusion, the prosecutors and the software vendor insisted that it was a secret. They argued that the defense team shouldn’t be allowed to look at how the software actually worked, because the vendor has a commercial interest in preventing competitors from knowing its trade secrets.

The court correctly ruled in favor of the defendant’s right to understand and challenge the software being used to implicate him. The code will not be publicly disclosed, but will be made available to the defense team. The defense needs this information about TrueAllele so that it can fairly participate in a procedural step known as a Frye hearing, used to ensure that a defendant’s rights are not undermined through the introduction of unreliable expert evidence.

In previous instances, defense experts have found fatal flaws in this kind of software. For instance, a complex DNA analysis program called “FST” was shown to have an undisclosed function in the code with the potential to tip the scales against a defendant. After the defense team found the issue, journalists at ProPublica persuaded the court to have the source code disclosed to the public.

This issue has arisen all around the country, and we have filed multiple briefs in different courts warning of the danger of secret software being used to convict criminal defendants. No one should be imprisoned or executed based on secret evidence that cannot be fairly evaluated for its reliability, and the ruling in this case will help prevent that injustice.