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Creating Informative DNA Libraries Using Computer Reinterpretation of Existing Data

R. David and M.W. Perlin, "Creating informative DNA libraries using computer reinterpretation of existing data", Northeastern Association of Forensic Scientists 2011 Annual Meeting, Newport, RI, 2-Nov-2011.


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Abstract

Forensic analysts work hard producing DNA data from complex biological evidence. They then expend further effort interpreting their data. However, current DNA interpretation guidelines can limit the amount of information that they are permitted to report. As more challenging data (e.g., mixed, low-level, degraded) enters the laboratory workflow, we see scientists working ever harder to extract diminishing identification information.

Computer interpretation using probabilistic genotypes is now allowed under the SWGDAM guidelines (Section 3.2.2). The computer can use validated quantitative models, instead of qualitative thresholds, to interpret and match the DNA evidence. Therefore, a computer assistant enables an analyst to extract all the information present in their data.

In projects with two separate labs, Cybergenetics used the TrueAllele® computer technology to re-interpret existing DNA evidence data. Probabilistic genotypes provided higher match statistics of use to prosecutors, whereas human interpretation based on 2010 SWGDAM guidelines often produced no match information at all. TrueAllele computer interpretation preserves (on average) a million times more identification information, as measured by DNA match statistics.

One DNA laboratory was in a large state, while the other was in a small county. Cybergenetics processed about 150 highly complex cases over a period of 4 months for the large state. These cases routinely included 3 and 4 person mixtures, often with low amounts or degraded DNA. Cybergenetics processed the DNA case data in large batches as they arrived, creating a library of computer-interpreted DNA evidence. Once the results were needed for court, Cybergenetics would then further examine the results, and prepare case reports which the lab would forward on to law enforcement agencies. The computer-inferred match statistics were generally appreciably larger than the human interpretation results.

TrueAllele DNA interpretation has been successfully introduced as evidence in state and federal courts. The TrueAllele match results have led to convictions and plea bargains; it has also excluded suspects from DNA evidence. Cybergenetics has been providing expert testimony, and is now training lab analysts to testify about TrueAllele results on their own data. More accurate TrueAllele interpretation has transformed cases with weak DNA information into evidence that could be effectively used in the criminal justice system. Better scientific information can better protect people from crime.

Society expects crime labs to process ever-increasing amounts of challenging DNA evidence. Computer interpretation empowers forensic analysts to use all their hard won DNA data to make positive identifications. The public-private collaboration between the forensic lab and Cybergenetics in this study has meant that the identification information residing in existing DNA data could be successfully extracted by computer, and then introduced as evidence in court.