DNA Continued from page 27 As the parameters of the hearing were limited by court order to an examination of the number of contributors, Dr. Shapiro focused on three main points of contention: (1) the sample in this case was indeed a low copy DNA sample; (2) the dropout rates employed by OCME were artificially low; and (3) the sample was likely a four person mixture as well as a ¨Type C¨ mixture and thus not suitable for comparison in the FST per OCME written protocols prohibiting comparison when an ¨excessive number of unlabeled peaks¨ are shown (Mr. Herman testified he did not look at the electronic data and had no idea what those peaks were). The importance of demonstrating that this was a low copy sample was that all of the stochastic effects were clearly seen in the genotyping results (peak height
variability, dropout and/or drop in of alleles, reproducible unlabeled peaks below threshold). If this was not a low copy number sample exhibiting drop-
Single source DNA is virtually conclusive; DNA mixtures of multiple contributors not so. out, Mr. Joseph would be excluded since two of his alleles were missing at a locus in each run. With respect to OCME´s dropout rate, Dr. Shapiro testified that they were clearly too low for the sample in this case. Even though Mr. Herman didn’t know the dropout rates, he entered values into FST which produced dropout
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parameters that would expectedly show, at most, six dropout or drop in events. Dr. Shapiro´s locus by locus examination of the electropherogram baseline illustrated high dropout, with as many as 35 additional possible alleles to be called, thus increasing the likelihood there were four contributors. Dr. Shapiro was permitted to testify as to degradation of the sample, stacked alleles and the difference between touch DNA and purposive mixtures. That all of these contributed to the assertion that this sample had at least four contributors is critical because ¨characterizing¨ and running a four person mixture as a three person mixture in FST will yield unreliable results. Moreover, the effect of using OCME´s artificially low and incorrect dropout rate on the final likelihood ratio is magnified because the dropout rate is factored into the computer calculations at each locus, replicate and genotype used, throwing denominator values off by the thousands and skewing probabilities by the millions. Late in 2017, a US District Court judge removed the protective order surrounding FST´s source code (¨the black box¨) and upon examination, it was discovered that the FST had incorporated a ¨corrective¨ measure which involved the dropping of a locus from the calculations. Justice Lewis was made aware of this development. On August 30, 2018 Justice Lewis ordered that the mixture sample in this case be re-tested, as The People did not conclusively establish at the hearing that there were only three contributors. Specifically, a 50 RFU threshold was ordered to be used in said re-testing in
Atticus | Volume 31 Number 2 | Fall 2019 | New York State Association of Criminal Defense Lawyers