Arizona Department of Public Safety begins using STRmix™

The Arizona Department of Public Safety Scientific Analysis Bureau will begin using STRmix™, sophisticated forensic software capable of resolving mixed DNA profiles previously thought to be too complex to interpret.

Introduced in 2012, STRmix™ has proven to be highly effective in producing usable, interpretable, and admissible DNA results in a wide range of criminal cases, including violent crime, gun, and sexual assault cases.

STRmix™ has also been instrumental in helping to solve cold cases in which evidence originally was dismissed as inconclusive, in exonerating individuals in post-conviction cases, and in excluding individuals wrongly associated as the source of crime scene evidence.

“Demand for STRmix™ has been extremely high due to its effectiveness in helping to solve crimes and clear caseloads,” 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™. To date, STRmix™ has been used to interpret DNA evidence in more than 220,000 cases worldwide, including 83 successful admissibility hearings.

STRmix™ works by running DNA test data through a wide range of probability models, using more of the DNA profile than ever before possible to calculate a likelihood ratio (LR) which is then weighed against coincidence to resolve complex DNA mixtures. It relies on proven methodologies which are used routinely in computational biology, physics, engineering, and weather prediction.

The Arizona Department of Public Safety Scientific Analysis Bureau joins 63 other local, state, federal, and private forensic laboratories throughout the U.S. which are currently using STRmix™ to interpret complex DNA profiles. Agencies making use of STRmix™ include the FBI, the Federal Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF), and the U.S. Army Criminal Investigation Laboratory (USACIL).  

The Scientific Analysis Bureau provides forensic services to all police agencies in Arizona. Those services include the scientific analysis of evidence, technical crime scene assistance, secure storage of evidentiary items, training, and expert testimony. The bureau has four separate regional laboratories: the Central Regional Crime Laboratory located in Phoenix; the Northern Regional Crime Laboratory in Flagstaff; the Southern Regional Crime Laboratory in Tucson; and the Western Regional Crime Laboratory in Lake Havasu City. 

The team that created STRmix™ launched a new version, STRmix™ Version 2.8, in late 2020 following nearly a year of extensive development and testing. STRmix™ v2.8 features a top-down approach that enables users to set the number of major contributors to a mixed DNA profile in which there is interest, and then obtain the LR only for those contributors. This approach allows users to tackle more complex profiles faster. The new version of STRmix™ also contains improved modelling and memory usage.

The same team also recently launched two other products: an update of DBLR™, an application used with STRmix™ that allows users to undertake superfast database searches, visualize the value of their DNA mixture evidence, and carry out mixture to mixture matches, now allowing kinship analysis; and FaSTR™ DNA, expert forensic software that rapidly analyzes raw DNA data generated by genetic analyzers and standard profiling kits and assigns a number of contributors (NoC) estimate.

Together, STRmix™, FaSTR™ DNA, and DBLR™ complete the full workflow(external link) from analysis to interpretation and database matching.