Forensic Software Links Suspect to DNA Left on Victim’s Clothing

STRmix™ – sophisticated forensic software capable of resolving mixed DNA profiles previously regarded as too complex or degraded to interpret – has played a key role in solving the 1994 murder of a six-year-old in the UK.


Using STRmix™ to analyze DNA left on the clothes of Rikki Neave, the UK’s Cellmark Forensic Services was able to provide a link for James Watson, now 41, to his murder. Watson, who was only 13 when he strangled Neave and left his body in a wood in Peterborough, has been sentenced to life in prison.


The case remained unsolved until police reopened it as part of a cold case review in 2015 and, because of advances in the sensitivity of DNA profiling, Cellmark was able to recover DNA from tape lifts originally taken to recover fibers. Using STRmix™, Cellmark was able to analyze the mixed DNA profiles obtained and provide a link to Watson, who was later charged with the murder.


“The conviction of James Watson for killing Rikki Neave concludes an appalling unsolved crime almost 30 years after it happened,” says Clare Forsdike, a Senior Crown Prosecutor at the CPS. “Ultimately, a combination of evidence from DNA, post-mortem, soil samples, eyewitness testimony, and his [Watson’s] changing accounts proved overwhelming.”


Since its introduction a decade ago, STRmix™ has established a highly successful track record of producing usable, interpretable, and legally admissible DNA evidence in more than 380,000 cases worldwide. It is now being used in 103 forensic laboratories, including 77 in the U.S., all nine state and territory forensic laboratories in New Zealand and Australia, and forensic labs in Europe, the UK, Asia, the Middle East, Canada, and the Caribbean.


John Buckleton DSc, FRSNZ, Principal Scientist at the New Zealand Institute of Environmental Science and Research (ESR) and one of the developers of STRmix™, notes that STRmix™ “has been extremely effective in resolving violent crime and sexual assaults, as well as cold cases like that of Rikki Neave in which evidence which originally would have been regarded as inconclusive can now be analyzed and reported.” 


STRmix™ works by assessing how closely multitudes of proposed DNA profiles resemble or can explain an observed DNA mixture, relying on proven methodologies routinely used in computational biology, physics, engineering, and weather prediction.


“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.”


The success of STRmix™ has led the team behind its development to launch two related products which, when combined with STRmix™, complete the full workflow(external link) from analysis to interpretation and database matching. These products include DBLR™, an application which allows forensic labs to undertake superfast database searches, visualize the value of DNA mixture evidence, and carry out mixture-to-mixture matches; 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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