In this interview, we talk to Dr. John Buckleton about the increasing use of forensic DNA software in solving criminal cases. Dr. Buckleton is one of the developers of STRmix™, a sophisticated forensic software used to resolve mixed DNA profiles previously considered too complex to interpret.
- Q. For some time, DNA has been regarded as the gold standard when it comes to crime solving. Is there any downside to relying on DNA in criminal cases?
A. DNA profile interpretation is relatively simple when the DNA present is from one person. It becomes much more complicated, however, when the DNA present is in low amounts, has been aged or degraded, or is “mixed” – that is, from more than one person, especially if any of those persons are related. Beyond those issues, you always have to consider the human factor. Mislabeling DNA samples, misinterpreting test results, or accidentally transferring cellular material or DNA from one sample to another can all lead to false reports of a DNA match.
The bottom line is that while forensic DNA testing is overwhelmingly reliable, it has occasional shortcomings. Like any process that involves human interaction and some degree of subjective decision-making, DNA tests are not now – nor have they ever been – completely error-free.
- Q. How has forensic DNA software made a difference in analyzing these more complicated DNA samples?
A. Forensic DNA software has greatly improved the ability to interpret low-level, degraded, or mixed DNA samples with a significantly higher degree of speed and accuracy than previously possible. In a recent Florida case, for example, analysts used forensic DNA software to separate and interpret multiple profiles of DNA extracted from the clothes of a woman murdered in 2009. Nearly nine years after her death, the Sarasota County Sheriff’s Office was able to charge Delmer Smith with murder and sexual battery thanks in large part to this new DNA evidence.
- Q. How does forensic DNA software do that?
A. As you might imagine, each solution is somewhat different. STRmix™, for example, works by uploading data from DNA testing, using more information from the DNA profile than previously possible. The profile is then run through an array of probability models, and the results compared against a person or persons of interest. From there, a likelihood ratio can be calculated, weighed against coincidence. Ultimately, this can be used to resolve highly complex DNA mixtures previously considered too complex to interpret, with a high degree of confidence in the validity of the findings.
- Q. Are there concerns surrounding the use of forensic DNA software in criminal cases?
A. Some have charged that forensic DNA software is simply too new to rely on its results. While it’s true that this software has been in use for less than a decade, it is equally important to recognize that this software is based on probability models and Markov Chain Monte Carlo methods in use since World War II. These models are widely used in everything from computational biology and weather prediction to physics, engineering, and the stock market.
Questions have also been raised about whether DNA software has been properly reviewed and validated. Peer-reviewed scientific journals, in fact, have published numerous scientific papers about various kinds of sophisticated DNA software. Internal validations have also been carried out by all labs in current casework, while both the International Society for Forensic Genetics and the Scientific Working Group on DNA Analysis Methods have published validation guidelines.
- Q. Would you say then that the benefits outweigh any issues or concerns?
A. Absolutely. STRmix™, which I helped to develop, significantly improves the ability of forensic analysts to contribute to criminal investigations in which DNA evidence previously was considered too complex to interpret. Ultimately, it helps to resolve the previously unresolvable. STRmix™ also includes a function that allows the software to match mixed DNA profiles directly against a database. This represents a major advance for cases in which there are no suspects and there is DNA from multiple contributors in a single sample.
- Q. Do those advantages give you a competitive edge over competing products?
A. Yes. Compared to other forensic DNA software, STRmix™ does not need to run on a dedicated server, making it both cost-effective and easy to use. STRmix™ is also able to produce results faster, mostly in minutes rather than hours unless the DNA profile is extremely complicated. Perhaps most important, because it can be easily explained in criminal court proceedings, STRmix™ is preferred by DNA analysts and more readily accepted in the criminal justice system.
- Q. What agencies now use STRmix™?
A. Right now, 30 U.S. forensic labs routinely use STRmix™ in resolving DNA profiles. These include everything from federal agencies such as the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) and the FBI to state and local agencies, including the Michigan State Police, Texas Department of Public Safety, and the California Department of Justice. STRmix™, which recently celebrated its fifth anniversary of use in live casework, is also in various stages of installation, validation, and training in 60 other U.S. labs.
- Q. What does the future look like for STRmix™ and other forensic DNA software?
A. In the five short years since it was introduced, STRmix™ has moved from being an experimental technology to the broadly accepted norm in cases in which forensic DNA software is required to resolve mixed DNA profiles. I expect use will continue to grow in the future as the software is continually improved and new features and functionality added.
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). Dr. Buckleton’s casework experience covers 33 years the UK, US, Australia, The Netherlands, and New Zealand. He has examined more than 2,000 cases and testified over 200 times. He has also co-authored over 180 publications in the forensic field focused on shoeprints, firearms, DNA, blood grouping, tool marks, fire debris analysis, glass, and paint.
