Ground-Breaking Forensic Software Will Be Used to Examine Complex DNA Evidence

The Metropolitan Police Department, City of St. Louis is the 69th organization in the U.S. to approve the use of STRmix™, sophisticated forensic software capable of resolving mixed DNA profiles that previously were regarded as too complex or degraded to interpret.


With nearly 2,000 employees, the Department is the primary law enforcement agency for the city of St. Louis, MO. It plans to 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 legally admissible DNA evidence in a wide range of criminal cases. It has proven to be particularly effective in resolving violent crime and sexual assault cases, as well as cold cases in which evidence originally dismissed as inconclusive was able to be reexamined.


 “To date, STRmix™ has been used to interpret DNA evidence in more than 300,000 cases worldwide,” 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™.


According to Buckleton, STRmix™ relies on proven methodologies routinely used in computational biology, physics, engineering, and weather prediction to assess how closely multitudes of proposed profiles resemble or can explain an observed DNA mixture.


“The probability of the observed DNA evidence can be calculated by assuming the DNA originated from either a person of interest or an unknown donor,” Dr. Buckleton explains. “These two probabilities can then be presented as a likelihood ratio (LR), inferring the value of the findings and level of support for one proposition over the other.”


In addition to the Metropolitan Police Department, City of St. Louis, STRmix™ is currently being used in the U.S. by such well-known agencies as the FBI and the Federal Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF). Internationally, nine state and territory forensic laboratories in Australia and New Zealand, and 14 labs in other countries including the U.K., Ireland, Canada, Finland, Switzerland, and Denmark are now using STRmix™.


A new version of STRmix™, Version 2.9, was recently launched. STRmix™ v2.9 contains a number of new features, including: the introduction of a batch maker mode, allowing multiple interpretations to occur simultaneously and database search templates; memory usage improvements, which are particularly significant in dealing with higher order DNA profile mixtures; and improvements to biological modelling calculations designed to improve the modelling of stutter peaks.

The success STRmix™ has enjoyed to date led the team behind its development to introduce two related products which in combination with STRmix™ complete the full workflow(external link) from analysis to interpretation and database matching:

  • DBLR™, an application which when used with STRmix™ allows forensic laboratories 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 which rapidly analyzes raw DNA data generated by genetic analyzers and standard profiling kits and assigns a number of contributors (NoC) estimate.

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