A U.S. District Court for the Eastern District of New York has denied a defendant’s motion to preclude expert testimony regarding the results of a DNA analysis produced by using STRmix– sophisticated forensic software used to resolve mixed DNA profiles.
Noting that “courts have overwhelmingly admitted expert testimony based on STRmix results,” District Court Judge Sterling Johnson, Jr. rejected defense concerns over the DNA analysis of a hat and bandana allegedly worn by the perpetrator of an attempted robbery in Eastern District of New York v. Tambhia Tucker (18 CR 0119 (SJ)).
The Office of the Chief Medical Examiner for New York City determined with a high degree of support that the defendant was included as a contributor to the DNA recovered from both the hat and the bandana.
In denying the motion to preclude, Judge Johnson pointed out that STRmix™ “is currently in use in over 40 states and federal laboratories in the United States and in at least 13 other countries.”
The order went on to state, “The software and its underlying principles have been peer-reviewed in more than 90 articles,” while “knowledgeable bodies,” such as the DNA Subcommittee of the New York State Commission on Forensic Science, “have evaluated the software and approved its use.”
While the court recognized there may be gaps in the understanding of the full reliability of STRmix™ and probabilistic genotyping more broadly, it concluded, “In recent years, confidence in the reliability of STRmix™ has only grown.”
The defense motion relied largely on a September 2016 report by the President’s Council of Advisors on Science and Technology (PCAST) which highlighted shortcomings in the field of forensic science, including DNA testing. The court, however, noted that the PCAST report’s concerns over DNA testing applied to DNA mixtures from three or more contributors. Mixtures in the current case came from only two contributors.
Since its introduction in 2012, STRmix has been used to interpret DNA evidence in more than 120,000 cases around the world. It is now being used regularly in 53 forensic labs throughout the U.S., while more than 60 other U.S. organizations are in various stages of STRmix™ installation, validation, and training.
“Forensic labs are turning to STRmix™ because of its success in producing usable, admissible DNA evidence in a wide range of criminal cases,” says John Buckleton DSc, FRSNZ, Forensic Scientist at the New Zealand Institute of Environmental Science and Research (ESR) and one of the developers of STRmix.
Dr. Buckleton notes that labs using STRmix are reporting an increase of interpretable DNA in gun cases from about 40% to more than 70%. STRmix is also delivering a significantly higher rate of interpretable results in sexual assault cases.
A new version of STRmix, STRmix v2.7, was introduced in late 2019. STRmix v2.7 includes several new features in response to improvements recommended by forensic labs to better address the on-the-job needs they regularly encounter.
DBLR, an application used with STRmix, was also introduced last year. DBLR allows users to undertake superfast database searches, visualize the value of their DNA mixture evidence, and carry out mixture to mixture matches.