Forensic Software Produces Usable, Interpretable, Legally Admissible Crime Scene Evidence

The St. Louis County Police Department recently became the 75th organization in the U.S., and the 101st in the world, to use STRmix™ forensic software in its scientific testing of crime scene evidence.    


Capable of resolving mixed DNA profiles previously regarded as too complex or degraded to interpret, STRmix™ has established a highly successful track record of producing usable, interpretable, and legally admissible DNA evidence in more than 380,000 cases worldwide since its introduction in 2012.


STRmix™ 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.


The St. Louis County Police Department is the largest county police agency in Missouri, with primary responsibility for law enforcement and investigations within unincorporated St. Louis County, as well as contract municipalities throughout the state. The St. Louis County Crime Laboratory provides scientific analysis of physical evidence for the County Police Department, as well as nearly 90 other municipal police agencies within St. Louis County.


STRmix™ works “by assessing how closely multitudes of proposed profiles resemble or can explain an observed DNA mixture,” says John Buckleton DSc, FRSNZ, Principal Scientist at the New Zealand Institute of Environmental Science and Research (ESR) and one of the developers of STRmix™.


Applying the same statistical methods routinely used in computational biology, physics, engineering, and weather prediction, STRmix™ calculates the probability of the observed DNA evidence by assuming the DNA originated from either a person of interest or an unknown donor. These probabilities are then 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 St. Louis County Police Department, 74 other forensic organizations in the U.S. – including those operated by the FBI and the Federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) – currently use STRmix™. STRmix™ is also being used in all nine state and territory forensic laboratories in New Zealand and Australia, as well as in forensic labs in Europe, the United Kingdom, Asia, the Middle East, Canada, and the Caribbean.


The STRmix™ team recently launched version 2.10 of its forensic software following extensive technical development and testing. STRmix™ version 2.10 contains a number of new features, including the introduction of a Visualize Weights module to help forensic analysts investigate DNA interpretation results and additional improvements to dropout modelling which will allow crime labs using FaSTR™ DNA to set a low, or even no, analytical threshold.


FaSTR™ DNA, which was also developed by the STRmix™ team, seamlessly integrates with STRmix™ (when in use) to rapidly analyze DNA profiles and assign a Number of Contributors (NoC) estimate.


In addition to STRmix™ v2.10 and FaSTR™ DNA, the STRmix™ team developed and  previously launched DBLR™, an application that when used with STRmix™ allows forensic labs to undertake superfast database searches, visualize the value of DNA mixture evidence, and carry out mixture-to-mixture matches and extensive kinship analyses. Together, FaSTR™ DNA, STRmix™, and DBLR™ complete the full workflow(external link) from analysis to interpretation and database matching.

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