A Colorado court has denied a defendant’s motion to exclude expert testimony regarding DNA evidence produced by STRmix™ -- sophisticated forensic software used to resolve mixed DNA profiles previously thought to be too complex to interpret.


The DNA evidence generated by STRmix™ indicated “very strong support” for the prosecution’s contention that DNA from the defendant, Trinidad Nunez, was present on a handgun linked to distribution of methamphetamine. Both the handgun and the illegal narcotics were found during a motor vehicle search following a traffic violation.


Relying on the standards for determining admissibility of expert testimony established in People v. Shreck (22 P.3d 68 Colo. 2001), Colorado’s District Court of Weld County ruled in Colorado v. Nunez (Case No. 18CR 515, Div: 11) that “STRmix™ has been sufficiently tested and found reliable; It has been subjected to significant peer review and publication; And the potential rate of error … are reasonably reliable.”


The court continued, “Suffice it to say, STRmix™ is generally accepted in the field of DNA and there exists the specialized literature dealing with the technique to determine NOC [the number of contributors] from multiple experts in the field of forensic science.” Moreover, “Colorado and other states have determined that probabilistic genotyping software, including STRmix™, is reliable and admissible.”


Since its introduction in 2012, STRmix™ has been used to interpret DNA evidence in more than 120,000 cases around the world. It has also been used successfully in numerous U.S. court cases, including 35 successful admissibility hearings.


STRmix™ is currently being used by forensic labs at 55 U.S. agencies – including the FBI and the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) – and is in various stages of installation, validation, and training in more than 60 other U.S. organizations.


John Buckleton, DSc, FRSNZ, one of the developers of STRmix™, points out that forensic labs increasingly are turning to STRmix™ “because it greatly improves the usability of DNA to produce evidence in a wide range of criminal cases. Organizations using STRmix™ are reporting an increase of interpretable DNA in gun cases from about 40% to more than 70%.”


According to Buckleton, STRmix™ is also proving to be highly effective in delivering a significantly higher rate of interpretable results in sexual assault cases.”


A new version of STRmix™, STRmix™ v2.7, was introduced late last year. 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.

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