A new article in the Boston University Law Review offers the following warning:
[E]xpansive police arrest authority–and the desire to continually enlarge identity evidence databases at very little cost in time and expense–should give pause for several reasons. First, contrary to common public perception, DNA is not infallible. Rather, like other evidence, it is subject to human error, bias, and malfeasance, and has figured in several wrongful accusations and convictions. As Professor David Kaye notes in his recent book:
How probable is it that two, correctly identified DNA genotypes would be the same if they originated from two unrelated individuals? By definition, [such matches] do not consider any uncertainty about the origins of the samples (the chain-of-custody issue), about the relatedness of the individuals who left or contributed the samples (the identical-alleles-by-descent issue), or about the determination of the genotypes themselves (the laboratory-error issue).
Wayne A. Logan, Policing Identity, 92 B.U. L. Rev. 1561, 1580-89 (2012) (footnote numbers omitted).
Having searched without success for a single case in the U.S. of a false conviction based on DNA evidence from a database search,1 I was puzzled. Could I have missed several false convictions arising from erroneous DNA testing? Did these cases involve database trawls, where observer “bias” is not normally an issue?
Being a lawyer, I did what any reader of law review articles must do. I turned to the footnotes. The footnote on false convictions as a reason to constrain DNA databases reads as follows:
See Greg Hampikian et al., The Genetics of Innocence: Analysis of 194 DNA Exonerations, 12 Ann. Rev. Genomics & Hum. Genetics 97, 107 (2011) (mentioning existence of at least fifteen exonerations in which DNA resulted in conviction).
If Professor Logan (and the source-citation reviewers of the Boston University Law Review) are correct, Professor Hampikian discovered at least 15 cases of DNA evidence that resulted in false convictions. How could I have missed all these case in my earlier postings?
The Genomics and Human Genetics review article plainly does not even begin to support the claim that DNA testing produced 15 false convictions. It merely states that among previously analyzed cases of postconviction exonerations, “there were at least 15 cases where DNA was tested prior to conviction.” Hampikian et al., supra, at 107. Let’s look at the outcomes of this DNA testing, as presented by Dr. Hampikian and his colleagues:
- The cited article does not even discuss the outcome of the DNA tests in two of the 15 cases because there were no “transcripts or other accurate information on the DNA results available.” Id. Counting two cases on which there is no information as showing that contemporary DNA databases produce false convictions is surprising.
- “The majority of these cases included proper testimony, with DNA results that excluded the exoneree (9 of the 13 cases). These exclusions were explained away by the state in various ways–perhaps the defendant had an unknown codefendant, the DNA could have come from a consensual sex partner, etc.” Id. Claiming that DNA databases should be constrained because most DNA typing accurately showed that a defendant was not the source of an incriminating sample is inane.
- “In 5 of the 13 cases, DQ alpha tests included the exonerees as possible contributors. In 4 of these 5 cases, however, more discriminating tests performed postconviction excluded the exonerees. In the remaining case, a second round of DQ alpha testing exonerated the defendant after it was discovered that the original lab analysis was incorrect.” Id. Before the DQA test was retired from forensic DNA testing, it was known to be relatively undiscriminating. See, e.g., Cecelia A. Crouse, Analysis of HLA DQ alpha Allele and Genotype Frequencies in Populations from Florida, 39 J. Forensic Sci. 731 (1994); NFSTC, DNA Analyst Training. Questioning databases stocked with CODIS profiles because a different, bi-allelic locus has different properties is silly.
- “There were four cases where improper DNA testimony was given at trial. In one, the analyst testified about a match based on DQ alpha testing; however, the analyst did not disclose that it was only a partial match. In another case, the analyst did not provide the proper statistic for the population included by the results of DQ alpha testing.” To be sure, “improper” testimony is deplorable, but it is not clear that the analyst in the first case incorrectly stated the implications of the match or, more importantly for worries about databases, that analysts working with database matches would give incorrect estimates of genotype frequencies.
- “In a third case, the analyst testified that the DNA matched the exoneree, but failed to disclose an additional exclusionary DNA result.” Withholding exculpatory evidence of any sort–DNA, fingerprint, toolmark, eyewitness, or anything else–is unconscionable and unconstitutional. But it is not much of an argument against inclusive DNA databases.
- “In the final case, the analyst misinterpreted the results of the testing (which was performed incorrectly–failing to separate the male and female DNA during differential extraction), falsely including the exoneree as a source of the DNA when in fact he should have been excluded.” Yes, if crime-scene DNA is mistyped, and if this error goes unnoticed, a database match could result.
Can DNA databases produce false convictions? Of course they can. Police can commit perjury about DNA evidence, just as they can about other evidence. If there were no databases, it might be slightly harder to fabricate such impressive evidence. DNA evidence, like all evidence, “is subject to human error, bias, and malfeasance.” So are law review articles. (And so are blog postings–corrections are welcome).
1. David. H. Kaye, Have DNA Databases Produced False Convictions?, Forensic Science, Statistics, and the Law, July 7, 2012 (cross-posted to The Double Helix Law Blog); David H. Kaye, Genetic Justice: Potential and Real, Forensic Science, Statistics, and the Law, , June 5, 2011 (cross-posted to The Double Helix Law Blog).
Cross-posted to Forensic Science, Statistics, and the Law.