Forensic Software Resolves Complex DNA Profiles in Criminal Cases

STRmix™, sophisticated forensic software used to resolve mixed DNA profiles previously thought to be too complex to interpret, has been approved for use by the Indian River (Florida) Crime Laboratory. 


The Laboratory, which is overseen by local law enforcement agencies within the 19th Judicial Circuit, will use STRmix™ in its scientific testing of crime scene evidence.


Since its introduction nearly a decade ago, STRmix™ has established a highly successful track record of producing usable, interpretable, and admissible DNA evidence in a wide range of criminal cases.


“Relying on proven methodologies routinely used in computational biology, physics, engineering, and weather prediction, STRmix™ has been used to interpret DNA evidence in more than 220,000 cases worldwide,” explains John Buckleton DSc, FRSNZ, Forensic Scientist at the New Zealand Institute of Environmental Science and Research (ESR) and one of the developers of STRmix™.  


According to Dr. Buckleton, STRmix™ has been particularly effective in the resolution of violent crime, gun, and sexual assault cases, as well as cold cases in which evidence originally dismissed as inconclusive was able to be reexamined.


STRmix™ works by running DNA test data through a wide range of probability models. Using more of the DNA profile than ever before possible – including low-level, degraded, or mixed DNA samples – STRmix™ calculates a likelihood ratio (LR) which is then weighed against coincidence to resolve complex DNA mixtures with an extremely high degree of accuracy.


The success STRmix™ has had to date in contributing to case resolution has led to its widespread adoption in forensic laboratories around the world. STRmix™ currently is being used in 65 local, state, federal, and private labs throughout the U.S., including the FBI and the Federal Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF). It is also in use in all nine state and territory labs in Australasia and labs in 13 other countries, including England, Scotland, Ireland, Finland, Denmark, and Canada.


Late last year, Dr. Buckleton and his fellow STRmix™ co-developers, Jo-Anne Bright (also of ESR) and Dr. Duncan A. Taylor of Forensic Science SA (FSSA), introduced STRmix™ Version 2.8 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 STRmix™ 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.

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