Texas prisoner close to exoneration after ground-breaking DNA analysis

A Texas man who was convicted on a charge of murder 10 years ago could be just weeks away from a complete exoneration thanks to ground-breaking DNA analysis that relies on a computer algorithm.

Lydell Grant, 42, was 7 years into his life sentence when in November 2019 he was released on bail. DNA evidence collected from the fingernails of his purported victim, Aaron Scheerhoorn, was re-examined by a proprietary software, which conclusively ruled him out as a suspect.

When the evidence was plugged into the FBI’s vast Combined DNA Index System, or CODIS, it produced a match. According to police, the new suspect, Jermarico Carter, has since confessed to stabbing Scheerhoorn outside a Houston gay bar in 2010.  

Grant’s case has sparked a debate in scientific and legal circles over the use of a new type of DNA analysis known as probabilistic genotyping. It uses mathematical algorithms instead of manual methods, especially in instances where the tested sample includes a DNA mixture from multiple people, reports NBC News.

What is probabilistic genotyping in DNA testing?

Unlike standard DNA testing, which requires a scientist to interpret the electronic data, probabilistic genotyping uses mathematical algorithms run on supercomputers to untangle complicated DNA samples, rather than discarding them for being inconclusive. Only a handful of private companies on the market offer these services to law enforcement agencies, including Cybergenetics in Pittburgh, and STRMix in California.

Cybergenetics helped clear Grant of murder by using its software, TrueAllele, to statistically analyze DNA samples. In this case, his DNA was excluded from evidence found under the victim’s fingernails with a one in ten trillion likelihood ratio.

This emerging approach to DNA testing relies on statistics and reduces subjectivity in the interpretation of results. However, legal experts argue that the companies using this new technique should be more transparent and reveal their methodology, so that both prosecutors and attorneys have equal access. The emergent technology has come under scrutiny by criminal defense lawyers and experts, because the source code of probabilistic genotyping programs is proprietary. In addition, the few private companies that are spearheading this approach have been reluctant to fully explain how it works, citing stiff competition in the marketplace.

Grant has emerged as a poster child of probabilistic genotyping, given that his case revolved around a mixture of DNA evidence belonging to the victim and an unknown male. Houston’s police crime lab, using traditional DNA analysis, was unable to conclusively say that the unknown male was Grant. In addition, he had an alibi for the night of Scheerhoorn’s murder, but several witnesses picked him out of a police lineup, ultimately leading to his conviction.

Mike Ware, Executive Director of the Innocence Project of Texas, became convinced that Grant’s DNA could not have been part of the sample, which the Houston Police Department’s crime lab failed to fully interpret. According to the Innocence Project, mistaken eyewitness identifications contributed to more than 70% of over 360 wrongful convictions in the USA that have been overturned by post-conviction DNA evidence.

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