By John Buckleton
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City, county, and state forensics labs increasingly are using sophisticated forensic DNA interpretation software. Forensic software’s ability to extract evidence from microscopic or mixed traces of DNA not only is contributing to criminal investigations in which DNA evidence previously was considered too complex to interpret, but also proving to be highly effective in cracking cold cases.

As a result, the findings of these analyses are being used to identify criminal activity with a high degree of confidence in their validity. In a recent Michigan case, for example, sophisticated DNA software interpreted the profile obtained from sweat inside a sneaker left behind at a crime scene, providing key evidence in an armed robbery case. The same software was recently used to isolate the defendant’s DNA in evidence presented in a Brooklyn, New York murder case, resulting in a conviction.   

Undoubtedly, forensic DNA software has improved the ability of forensic analysts to interpret low-level, degraded, or mixed DNA samples. By running DNA test data through a range of probability models and using more of the DNA profile than previously possible, forensic DNA software is able to calculate a likelihood ratio, weighed against coincidence, to resolve DNA mixtures previously regarded as “unresolvable.”

But does this software represent the advance in DNA testing its supporters claim? Let’s take a look at the issues typically raised with respect to forensic DNA software.   

• It’s too new. Pointing to the Frye Standard, detractors claim forensic DNA software fails to meets the general acceptance test. While it’s true this software has been used for less than a decade, it is based on probability models and Markov Chain Monte Carlo methods employed since World War II and used in everything from weather prediction to physics, engineering, and the stock market.

• Peer Review. Opponents also question whether forensic software has been validated independently and subject to peer review. In fact, numerous scientific papers have been published in peer-reviewed scientific journals. Internal validations have been carried out by all labs in current casework, as required by their accreditation. Beyond that, the International Society for Forensic Genetics published guidelines for validating software in 2016, while the Scientific Working Group on DNA Analysis Methods (SWGDAM) has produced guidelines for validating probabilistic genotyping tools

• Secrecy. Detractors charge that because the algorithms used in forensic DNA software are sometimes secret, they are dealing with a black box situation in which the software’s functioning cannot be properly reviewed. While this is true for some DNA software, others make code available under a non-disclosure agreement. In addition, all of its algorithms have been published and are freely available. Other DNA software is open source, making its code and algorithms available for users to explore and improve.

• Miscodes. Another potential issue is the miscodes occasionally found in forensic software. Bottom line, no complex software is free of miscodes. The miscodes that have materialized, however, have occurred on the edges of normal usage and have had no substantial effect on the statistic given. So while an error-free guarantee probably doesn’t exist, it is possible to guarantee that normal usage has been extensively tested and is appropriate for use by fully trained forensic experts.  

Other questions have been raised – and will continue to be raised – with respect to sophisticated forensic DNA software. It’s the nature of anything new. The bottom line, though, is that forensic labs now have a highly effective tool at their disposal. And while the future will see even more advances, the increasing acceptance and use of sophisticated forensic software undoubtedly will have a profound impact on their ability to solve previously unsolvable cases.

John Buckleton is a noted forensic scientist who has worked extensively in the DNA field as a member of New Zealand’s Institute of Environmental Science and Research Limited (ESR).