United States v. Cortorreal
| Decision Date | 07 April 2023 |
| Docket Number | 17-CR-438 (VEC) |
| Parties | UNITED STATES OF AMERICA, v. EDWIN CORTORREAL, Defendant. |
| Court | U.S. District Court — Southern District of New York |
Edwin Cortorreal is charged with murder in aid of racketeering in connection with a robbery during which the Government alleges Cortorreal shot and killed Kelly Diaz. See Superseding Indictment (Dkt. 537). Jury selection and trial is scheduled to commence on April 17, 2023. See Order (Dkt. 782). Mr. Cortorreal seeks to exclude DNA evidence collected from a cell phone battery found in the stairwell of the apartment building in which Diaz was killed. See Def. Mot. (Dkt. 636); Def. Supp. Mot. (Dkt 718).[1] Mr. Cortorreal argues that the New York City's Office of the Chief Medical Examiner (“OCME”) analyzed the DNA using unreliable methods rendering testimony related to the results of that analysis inadmissible. See id. The Government opposes the motion and argues that the DNA collection and analysis satisfy the Daubert standard for admissibility. See Gov. Opp. (Dkt. 644); see also Gov. Supp. Opp. (Dkt. 722). For the reasons discussed below, Defendant's motion is DENIED.
Mr Cortorreal moves to preclude testimony regarding the DNA that was collected from the cell phone battery because, he argues OCME's Low Copy Number (“LCN”) testing protocols are unreliable. Def. Supp. Mem. at 1 (Dkt. 718).
New York City's Office of the Chief Medical Examiner (“OCME”) is a nationally accredited forensic laboratory that, among other things, performs DNA testing in criminal cases. See O'Connor Decl. ¶ 7 (Dkt. 645). OCME is also accredited by New York State's Commission on Forensic Science (the “Commission”). See Tr. at 33:11-22 (Dkt. 710). The Commission develops standards for and accredits forensic laboratories in the state. See id. OCME is required to adhere to the quality assurance standards and guidelines established by the Scientific Working Group of DNA Analysis Methods (“SWGDAM”), a group run by the Federal Bureau of Investigation (“FBI”) that is comprised of approximately 50 scientists from forensic labs in the United States and Canada. Id. at 96:22-97:12; see also Gov. Opp. at 6 n.5 (Dkt. 644).
DNA analysis involves examining Short Tandem Repeats (“STR”); STRs are small segments of DNA. See Krane Decl. ¶ 8 (Dkt. 637-3). DNA analysis looks at the number of times a sequence of bases repeats at a particular location, called a “locus” (or plural, “loci”), in a strand of DNA. Id. A person inherits one allele at each locus from each biological parent.[2] Id. For example, if there are eight consecutive repeats of a sequence of bases at a particular locus, the DNA allele would be called an 8. Continuing the example, if at that same locus, the person also has ten consecutive repeats of a sequence of bases, the “allele call” for that locus would be 8, 10. See Tr. at 39:19-41:16 (Dkt. 710). As is relevant to forensic work, the alleles at the different loci comprise a person's DNA profile; a suspect's profile can then be compared to the DNA profile recovered from evidence to determine whether the suspect's DNA matches the DNA recovered from the evidence. See id. at 41:25-42:24.
OCME historically has performed two types of DNA testing: High Copy Number (“HCN”) and Low Copy Number (“LCN”). O'Connor Decl. ¶ 10 (Dkt. 645); Gov. Opp. at 6 (Dkt. 644) (citing United States v. Morgan, 53 F.Supp.3d 732, 736 (S.D.N.Y. 2014)).[3] Both types of testing involve four steps: (1) extraction (i.e., recovering DNA from human cells); (2) quantitation (i.e., measuring the quantity of DNA extracted); (3) amplification (i.e., copying the DNA multiple times to produce a greater quantity of DNA that can then be analyzed); and (4) analysis. Krane Decl. ¶ 8 (Dkt. 637-3); Gov. Opp. at 4 (Dkt. 644) (citing United States v. Jones, 965 F.3d 149, 155 (2d Cir. 2020)).
At the time OCME first performed its analysis on the DNA recovered in this case, OCME had been using LCN testing to analyze samples of DNA ranging from 5 to 100 picograms. See Tr. at 99:18-100:11 (Dkt. 710). OCME's protocols for LCN testing deviated slightly from its protocols for HCN testing. Id. 67:12-22, 87:17-88:1. For LCN testing, OCME divided the DNA sample into three aliquots, with each aliquot subject to 31 amplification cycles.[4] Krane Decl. ¶ 11 (Dkt. 637-3). After amplification, each aliquot produces a result known as a “replicate” or “triplicate.” See id.; Tr. at 84:11-25 (Dkt. 710). The goal of this approach is to account for the increased risk and prevalence of stochastic effects in LCN testing. Tr. at 84:11-25 (Dkt. 710); see also Gov. Supp. Opp. at 3 (Dkt. 722).
Both HCN and LCN testing have a risk of stochastic effects, which are random errors in genetic testing. See O'Connor Decl. ¶ 10 (Dkt. 645). Because of the small sample size of the source material and the triplicate amplification process, however, LCN testing has an increased risk of stochastic effects, which can make it more difficult to interpret the results of an electropherogram (“EPG”).[5] See Tr. at 75:17-23 (Dkt. 710); Krane Decl. ¶¶ 9-14, 20 (Dkt. 6373). Stochastic effects include so-called allelic drop-in and drop-out,[6] and peak height imbalance.[7]Id. LCN testing's amplification process can also result in elevated or exaggerated stutter, which can be mistaken for a true allele on an EPG. Id. ¶¶ 9, 14-15; Tr. at 1058:11-1059:3 (Dkt. 760).
The goal of the triplicate amplification process is to allow analysts to better assess EPGs to account for stochastic effects by examining three EPGs for each locus. Tr. at 77:5-14, 84:1188:15 (Dkt. 710). The triplicate amplification process increases the likelihood that true alleles will be seen, which reduces the risk that allelic drop-in or drop-out will have an impact on the analysis. See id. At a given locus, an allele that appears only once in the three amplifications may be indicative of allelic drop-in or elevated stutter. On the other hand, an allele that appears in two of the three amplifications suggests that its absence in the third is the result of allelic drop-out.
After amplification, DNA analysts examine the results of the EPG to assess whether the sample likely comes from one individual (a single-source sample) or multiple individuals (a mixture). See id. at 55:14-56:6 (Dkt 710). Although analysts have discretion in determining what to call an allele and what to disregard as a stochastic effect, Tr. at 262:22-263:10 (Dkt. 712), OCME's LCN testing protocols provide that if the sample contains at least three repeating alleles at a minimum of three loci, the sample must be considered a mixture, Gov. Opp. at 9 (Dkt. 644) (citing STR Results Interpretation Protocol at 20-24, 42-43, and 45-48);[8] see also Tr. at 145:17148:3 (Dkt. 710). After evaluating the results of each amplified replicate, the OCME analyst creates a composite DNA profile based on all alleles that appear in at least two of the three replicates.[9] Tr. at 88:2-15 (Dkt. 710).
If the analyst determines the sample to be a mixture of two or three contributors,[10] the analyst next determines whether one contributor's “DNA predominates, such that the analyst can identify a ‘major contributor'” and use that profile for comparison purposes as if it were a single- source sample. Gov. Opp. at 9-10 (Dkt. 644) (citing STR Results Interpretation Protocol at 43, 46-47); Tr. at 57:21-59:9 (Dkt. 710). Such a mixture is considered deconvolutable, meaning the analyst can interpret the EPG to discern a distinct DNA profile from the sample. Tr. at 57:2-58:10 (Dkt. 710). If, however, the contributors to a mixture are evenly balanced, then the mixture is deemed non-deconvolutable, meaning no major contributor can be identified. Id. at 59:15-60:7. To account for the increased risk of stochastic effects, and purportedly to make its interpretations “more conservative,” OCME will include an allele in the composite profile of a deconvoluted mixture only if the allele appears in all three replicates or if it appears in only two of the three replicates but the major alleles have peak heights within 50% of each other. Gov. Supp. Opp. at 4 (Dkt. 722); Tr. at 166:8-167:8 (Dkt. 710).
In sum: if the analyst is able to deconvolute the mixture to discern a major donor profile, the analyst may then compare that profile to a suspect's DNA profile to determine whether to include or exclude the suspect as a possible contributor. See Tr. at 57:2-58:10 (Dkt. 710).
The conclusions reached by the OCME analyst are subject to second-level review by an assigned technical reviewer. Dr. O'Connor, the Assistant Director of Forensic Biology at OCME, testified that technical reviewers at OCME “rarely” disagree with the initial outcome reached by the analyst. Tr. at 853:1-854:11 (Dkt. 760). He also acknowledged that OCME protocols do not require the technical reviewer to perform a “cold” second-level review - i.e., a review without knowing the conclusion reached by the analyst. See id.
To use LCN testing in criminal casework, OCME was required to undergo a validation process and obtain approval from the New York State Commission on Forensic Science. See Tr at 94:22-95:6 (Dkt. 710); O'Connor Decl. ¶ 7 (Dkt. 645). OCME developed its validation studies based, in part, on peer-reviewed research conducted by other laboratories around the globe that had been studying LCN testing. See Gov. Supp. Opp. at 4 (Dkt. 722) (citing GX-9, GX-10, GX-53, GX-54); Tr. at 91:11-94:18 (Dkt. 710). OCME conducted validation studies over the course of a four-year period to test the ability of LCN to analyze DNA samples of different quantities and from different sources reliably. See Tr. at...
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