Monday, November 6, 2017

FORENSIC EVIDENCE BACK IN THE NEWS (DNA ANALYTICS)

An interesting development in the area of algorithms being used to generate statistics on DNA:

A federal judge unsealed the source code for a software program that was used to compare DNA samples in New York City’s crime lab. In July 2016, Judge Valerie Caproni of the Southern District of New York determined in U.S. v. Johnson that the source code of the Forensic Statistical Tool, a genotyping software, “is ‘relevant … [and] admissible’” at least during a Daubert hearing—a pretrial hearing where the admissibility of expert testimony is challenged. Caproni provided a protective order at that time.

This week, Caproni lifted that order after the investigative journalism organization ProPublica filed a motion arguing that there was a public interest in the code. ProPublica has since posted the code to the website GitHub.

Probabilistic genotyping is used when comparing complex DNA samples, like mixtures. It does not define a DNA sample itself; rather, it is an interpretive software that runs multiple scenarios, like risk analysis tools used in finance, to analyze the sample. This contrasts with traditional DNA analysis, which analyzes whether a DNA type is present or absent.

While there are numerous public and proprietary genotyping software programs, ProPublica reports that the “FST was used to analyze crime-scene evidence in about 1,350 cases over about 5½ years.” The FST was phased out at the beginning of this year with the adoption of different software.