The underlying argument by the petitioner was that there had been a change in expert opinion which would render the original opinion “false evidence” under Pen. Code 1473(e)(1). In this case, the repudiated scientific evidence had to do with the manner in which complex DNA mixtures are interpreted.

For background purposes, it should first be explained that starting in 2010, laboratories were expected to begin changing the manner in which they interpreted complex mixtures as it had been determined through journal research and various mixture interpretation studies that the unrestricted Combined Probability of Inclusion statistic was being applied inappropriately by many forensic laboratories to some forensic DNA samples that consisted of mixtures of multiple individuals. Often touted as being the “more conservative” approach to mixture statistics, it was determined that the CPI method, when used inappropriately, could be overly inclusive – especially when dealing with low-level mixture data. For additional information on how the Scientific Working Group on DNA Analysis Methods (SWGDAM) guidelines changed the manner in which mixtures were interpreted see my previous article on my blog at www.ryanforensidna.com entitled “What in the World is Going on With Forensic DNA Mixture Analysis”.

I would argue that attorneys and their clients who have cases from around 2012-2013 or earlier may very well be dealing with an improperly (at least by today’s standards) interpreted mixture profile. The reason for this is that, even though laboratories changed their guidelines to comply with SWGDAM, many have chosen to cite a statement found in the introduction of the 2010 SWGDAM Interpretation Guidelines indicating that “the revised guidelines are not intended to be applied retroactively” art heir rationale for ignoring any case that was interpreted under the “old’ guidelines. Interestingly, even shortly after the SWGDAM guidelines were released, some in the forensic community were questioning the validity of this statement. For example, Jules Epstein, Associate Professor of Law at Widener University School of Law gave a presentation to attendees at the National Forensic Science Technology Center Mixture Interpretation Workshop held in March 2011 entitled, “The Law, Ethics, and DNA Interpretation”. He brought up several interesting points in his presentation including the fact that considering that these are “new guidelines”, does that mean that the old way of doing things was not good enough? Further, he argued that while SWGDAM can state that the guidelines are not to be applied retroactively, is this an appropriate response and is it actually enforceable? SWGDAM obviously does not have any precedence over our courts of law, for example.

Regardless, in my experience as a forensic DNA consultant who has reviewed hundreds of cases since the change in the SWGDAM guidelines, it is fairly unusual to see a forensic laboratory issue an amended report with new calculations based upon updated mixture interpretations.

So what did forensic laboratories do to address the changes in their protocols that have changed the way they interpret mixtures? Some laboratories chose to issue amended reports with updated conclusions for cases that had not yet gone to trial. Some laboratories opted to issue amended reports reflecting the new interpretation and statistical calculations only upon request from the prosecution (or possibly the defense, if they were aware of the changes to begin with). Some laboratories opted to inform the District Attorney’s Office of the changes and how those changes might affect their cases. Through a review of internal memos, it is clear that some laboratories chose to discuss the issue internally amongst themselves only, and opt to continue to testify to the old results even if they had updated their mixture interpretation guidelines to comply with SWGDAM.

It appears that the San Diego Police Department Crime Laboratory chose to recalculate the statistic upon request. However, if no request was made, analysts continued to testify to the “old” results at trials . That brings us back to the Writ of Habeas Corpus granted a few days ago in San Diego. Although the lab had changed their mixture interpretation guidelines to comply with SWGDAM a mere 4 or 5 days prior to the SPDD analyst offering his testimony in the second trial of the petitioner (the first had ended with a hung jury), there was no mention of the change in methodology either prior to his testimony, or while on the stand – even though the SWGDAM changes were repeatedly discussed by the defense and the defense DNA expert during the 2011 trial. Judge Rogers found this to be a Brady violation as, in his words, the crime lab personnel are considered to be part of the “prosecution team” and are therefore responsible for disclosing matters that may be considered favorable to the defense.

In this case, the reason the change in the methodology would be considered favorable to the defense is that upon reinterpretation of the mixtures in 2015, at the request of the defense attorney, the results went from including the defendant as a possible contributor to a mixture found inside two gloves to an inconclusive result for each glove, where the profile was deemed ineligible for comparison to any reference standard. In fact, a declaration prepared by the SDPD analyst stated “I would testify differently than I did at the trial in April 2011… Specifically, I would testify that due to the low level and unknown number contributors to each sample, a. No comparisons can be made regarding potential minor DNA contributors and b. No statistical calculations can be made regarding potential minor DNA contributors”.

What does this mean for the thousands of cases where mixtures have been interpreted the “old way”? The way that has since been shown to be overly inclusive? The way that has led to the closure – permanent or temporary – of at least two forensic DNA laboratories? The way that leaders in the field of forensic DNA analysis, including Dr. Bruce Budowle and Dr. John Butler, have warned against by stating that the CPI cannot handle possible allelic drop-out and cannot be used on stochastic level data with unknown numbers of contributors? That remains to be seen. Considering that less than 1% of petitions for Habeas Corpus are granted, Judge Rogers’ decision to grant the petition in a case involving the same mixture interpreted two different ways – pre-SWGDAM and post-SWGDAM – illustrates that this is a significant issue in the forensic DNA community and in the legal community.

In 2015 the Texas legal community was alerted to the very same issues being discussed in San Diego when mixtures were being reinterpreted due to a secondary issue with some errors in the population databases used to calculate statistics. When prosecutors noticed that at times there were vast differences between the prior calculation and the new ones, they realized there may be a significant issue – and they began to address this issue with the help of the Texas Forensic Science Commission. This was a great step for the legal community in Texas. But what about the rest of the country? When will attorneys, judges, and even laboratory analysts realize that the improper interpretation of low-level complex mixtures affects every jurisdiction and it is likely that nothing has been done over the past 7 years to rectify these issues? While not every mixture interpretation performed prior to the 2010 SWGDAM DNA interpretation guidelines is automatically incorrect, it stands to reason that there are a large number of mixture profiles that, if re-interpreted today, would yield results similar to the San Diego case detailed in this article wherein results would change from inclusion to inconclusive, or possibly even from inclusion to exclusion. The legal community around the country needs to be aware of these issues and to closely re-examine any cases that may have been subject to improper mixture interpretation.