ProPublica is asking a federal court for access to the source code for New York City’s proprietary DNA software, which some scientists and defense lawyers contend may be inaccurate in matching a defendant to a complex sample of genetic material. Known as a pioneer in analyzing the most difficult evidence from crime scenes, the New York City medical examiner’s office has processed DNA samples supplied not only by local police, but also by about 50 jurisdictions nationwide.
Employees developed the disputed software — known as the Forensic Statistical Tool, or FST — to analyze evidence consisting of multiple people’s DNA and determine the likelihood that a suspect’s DNA was present. According to the medical examiner’s office, FST was used in about 1,350 criminal cases from 2011 until this year, when it was phased out. The office has long kept the source code secret, successfully opposing requests in court by defense attorneys to examine it.
A motion ProPublica filed today in the Southern District of New York asks Judge Valerie Caproni to lift a protective order she had issued in a recent case, U.S. v. Kevin Johnson. While she became the first judge to require the lab to turn over the source code to the defense, her order barred parties in the case from sharing or discussing it.
As reported earlier this month by ProPublica and The New York Times, defense expert Nathaniel Adams, a computer scientist and an engineer at a private forensics consulting firm in Ohio, reviewed the code and found that “the correctness of the behavior of the FST software should be seriously questioned.” However, the versions of Adams’ affidavits available to the public were heavily redacted and the code itself remains shielded by the judge’s order. The medical examiner’s office characterized Adams’ criticisms as stylistic rather than substantive and said FST’s calculations were reliable.
FST played a key role in Johnson’s case. He was arrested after a police search found two guns in his ex-girlfriend’s apartment, where he sometimes stayed. The DNA lab in the medical examiner’s office found two people’s DNA on one gun; by FST’s calculation, it was 156 times more likely than not to contain Johnson’s DNA. The second gun had three people’s DNA and a formidable likelihood of 66 million. Johnson pleaded guilty to illegal gun possession and Caproni…