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Kamis, 30 Mei 2013

People v. Garcia and Low Template DNA (LT-DNA)

Recent postings (March 27, May 25) about the appeal of Amanda Knox and Raffaele Sollecito suggested that the court’s decision not to order more DNA tests on the kitchen knife was less a manifestation of bad judicial mathematics than a judgment about the possible costs and benefits of additional low template (LT-DNA) testing as perceived by court-appointed experts. As a publication of the Royal Statistical Society noted last year, “Many questions at the extremities of LTDNA technology remain unanswered, and scientific disputes between experts are sometimes ventilated in litigation.” (Puch-Solis et al. 2012, at 85 ¶ 60.20, discussing English Court of Appeal cases in ¶¶ 60.21 & 60. 22).

In the United States, appellate courts have yet to address the admission of LT-DNA results. The latest opinion I have seen comes from a trial court in Bronx County, New York. In People v. Garcia, 39 Misc.3d 482, 963 N.Y.S.2d 517 (N.Y. Sup. Ct. 2013), a woman was found suffocated, with a sock in her mouth, and bound, with duct tape binding her face and limbs. Pablo Garcia was charged with her murder and related crimes. A piece of the duct tape contained DNA from at least two individuals. The New York City Office of the Chief Medical Examiner (OCME) reported that the mixture “is 586 times more probable if the sample originated from this defendant and one unknown, unrelated person than if it originated from two unknown, unrelated persons.”

Now, it is easy to see how a murderer applying the tape would leave some DNA on it, but why would there be additional DNA from an “unknown” rather than from the victim? One would think that duct tape used to bind an individual would include that person’s DNA rather than “one unknown, unrelated person.” However, it could be—I am speculating here—that the sample came from duct tape wrapped on top of other duct tape rather than a piece attached directly to the skin. Would the additional DNA profile have come from someone in the factory where the tape was made? From someone besides the murderer who touched its edges after the package had been opened? These are the kinds of possibilities that need to be considered when dealing with extremely small quantities of “contact DNA.”

Hoping to exclude the LT-DNA evidence, Garcia requested a pretrial hearing on whether the OCME’s protocols for typing LT-DNA and computing likelihood ratios were generally accpeted in the relevant scientific community. Judge Nicholas Iacovetta denied the request. He found that Garcia failed to raise much doubt about general acceptance. He wrote that “There is nothing new or novel about LCN DNA profiling. It simply represents the application of accepted and reliable procedures [like PCR and electrophoesis] that are applied in a modified manner.”

This reasoning, which has been used in previous cases, seems far too facile, After all,
PCR-based STR profiling with capillary electrophoreses is generally accepted for the purpose of producing identifying profiles because experiments have demonstrated its validity and it fits into well-established theories of chemistry and biology. It satisfies the validity standard of Daubert for the same reasons. But this foundation might not extend to the domain of the smaller samples. A light microscope works wells for studying bacteria but its magnification is not adequate for viewing much smaller viruses. For that purpose, an electron microscope is required. Radar can track airplanes or flocks of birds, but the signal-to-noise ratio is too low for it to be useful in tracking the flight path of a solitary, high-flying butterfly. The radar equipment is identical, and the operator is no less skilled at interpreting what he sees on the screen, but the procedure has not been validated (and would not be valid) for butterfly tracking.

Likewise, in the case of touch DNA, the relevant question is not whether the instrumentation and chemicals are identical or whether the analysts are using the same standards for interpretation. It is whether the system has been validated in the range in which it is being used. This is not a question about how well a validated or generally accepted procedure worked on a particular occasion ... . It is a ... question about the ability, under the best of conditions, of the equipment and its operators to pick out a weak but true signal from the noise. Until this trans-case question is resolved, admissibility is unjustified under Frye and Daubert.
Kaye, Bernstein and Mnookin (2011, § 9.2.3 at 428).

These observations do not necessarily mean that all forms of LT-DNA profiling--including the OCME's methodology--should be held inadmissible under the general acceptance standard for scientific evidence followed in New York. They simply mean that one must look to suitable experiments published in scientific journals or other places where they would be subject to critical review by other interested scientists, to the testimony or published views of appropriate scientists who have studied the matter, and to other indications of general acceptance.

Judge Iacovetta did some of this scrutiny and concluded “[s]eparately ... that LCN DNA testing conducted by OCME and its [statistical analysis] are both generally accepted as reliable in the forensic scientific community.”

The bases for this separate conclusion, however, are not uniformly compelling. First, the court pointed to “a lengthy Frye hearing” conducted by another trial court that determined “that LCN DNA testing ... when properly performed, ... is generally accepted as reliable in the scientific community.” Before accepting the conclusion of another judge who did conduct an evidentiary hearing, however, a court should ensure that the hearing actually aired the views of a cross-section of the scientific community. Especially in the early days of a scientific technique, imbalanced hearings are not uncommon. For examples in the DNA area, see Kaye (2010).

Second, the Garcia opinion stated that “[o]ther New York trial courts have also admitted LCN DNA results in evidence after denying defense requests for a Frye hearing ... LCN DNA testing has been admitted in New York State trial courts over 125 times, and in a federal district court in the Southern District of New York without a Frye hearing and in courts of multiple other countries including Germany, The United Kingdom, Sweden and Switzerland.” Again, a history of usage—especially without any hearings on the necessary foundational research and with no meaningful appellate review of the trial rulings—is a weak indicator of scientific acceptance.

Third, the court noted that “[a]lthough OCME is the only government facility currently using LCN DNA testing, several private and academic laboratories, such as the University of North Texas, use LCN DNA testing. OCME ... has been certified to conduct LCN DNA testing since 2005, using it to help identify the remains of victims of the World Trade Center terror attack in 2001 ... .” This is better. Usage of a method outside the courtroom, especially in matters that supply feedback on how well the method works, helps establish acceptance. (However, more details demonstrating the equivalence of the other uses to the one in Garcia itself would have been helpful.)

Fourth, the court observes that “OCME's own validation studies of LCN DNA testing ... were examined and certified by the New York State Commission On Forensic Science (NYSCFS) in 2005” and that “OCME is also audited yearly.” Favorable review by outside scientific staff of the commission and an auditing organization of a suitable set of the validity studies (as opposed to audits to show that the laboratory follows its protocols, investigates and corrects problems, and the like) argues in favor of general acceptance.

Finally, in discussing the software the OCME developed to help interpret mixed, partial DNA profiles from small samples, the opinion alludes to "peer reviewed articles in professional journals such as the International Journal of Forensic Genetics." I am not familiar with a journal by this name, and it does not seem to have a web site. Perhaps the court was referring to papers in Forensic Science International: Genetics (Mitchell et al. 2011; Mitchell et al. 2012). See also Caragine et al. (2009). The best evidence of general acceptance of validated technologies is publication in established scientific journals followed (ultimately) by a cessation of debate over the findings.The OCME publications support the laboratory procedures as well as the software for interpreting the data from those procedures.

Focusing on the software (named FST), Garcia states that
Other software programs such as True Allele, Life TD, Forenism, and Locomation, a software tool designed in the 1990's, also use Bayes Theorem to perform functions similar to the FST. The difference is that the FST uses empirically established drop-in and drop-out rates generated by thousands of tests, rather than just estimating them, which makes the FST more accurate as a predictor of likelihood ratios.
At the risk of quibbling (an occupational and personal hazard), these programs do not "predict likelihood ratios." If they predict anything, they predict genotypes, and which program's LRs best express the probative value of the inferred genotypes depends on more than how each program handles drop-in and drop-out probabilities.

To sum up, even if is wrong to regard the application of established technologies to LT-DNA as a trivial variation that requires no further legal scrutiny to establish admissibility, it also appears that one can make a reasonable case for general scientific acceptance of LT-DNA typing as required under New York law. The Garcia opinion shows how one trial judge was convinced.

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