If crime scene evidence contains commingled DNA from different people, it can be too complex for crime labs to sort the mixture. Computer scientist Mark Perlin has developed a computer program called TrueAllele that separates the genetic types of each person in the sample so they can be compared with the DNA of suspects. Law-enforcement authorities are now turning to TrueAllele to make sense of mixed-up DNA.
In Allegheny County, Pennsylvania for example, authorities plan to use the program in the prosecution of a defendant who was charged of shooting two men and therefore could face the death penalty. Near the crime scene, investigators found a black bandanna, that a witness said was worn by the shooter. It contained a mixture of DNA from at least three people, that the county crime lab deemed too complex to analyze. TrueAllele however concluded that the defendants DNA was on the garment. According to the report on the software’s findings, this conclusion is 5.7 billion times more probable than a coincidental match to another, unrelated African American. The defendants lawyer now requested that his client can „challenge the validity and reliability of the methodology“ used by TrueAllele, including the source code.
And this is where the dispute starts:
Defense lawyers criticse that Mr. Perlin has not provided enough information about how TrueAllele works. They argue they can’t determine whether the software is erroneously linking their clients to crimes if they are unable to review the instruction the program gives the computer. They want to know the assumptions the software makes about sample degradation or how it isolates real signals from mere noise and demand access to the source code of the program.
Mr. Perlin on the other hand refuses to allow defense experts to review TrueAllele’s 170,000 lines of source code, calling them a trade secret. He further argues that the dozens of validation studies conduced on TrueAllele would offer far more insight into the program than the source code. Alternatively, his company Cybernetics offered to walk experts through the program on a computer and let them test a limited set of data.
Despite the challenges from defense lawyers, courts in at least six U.S. states have admitted TrueAllele test results into evidence.
Rebecca Weller, a fellow in Yale Law School’s Information Society Project, suggested a compromise: Defense experts should be allowed by the court to review the code and be forbidden from sharing it. „If the software is as bulletproof as its manufacturers claim, they have nothing to lose and only to gain from this additional scrutiny,“she said.
Source: The Wall Street Journal