United States v. Barton
8:14-cr-00496
| M.D. Fla. | Sep 14, 2016Background
- Defendant Robert W. Barton moved to exclude DNA evidence and expert testimony (Daubert motion) challenging the reliability of the government lab’s interpretation of an unknown mixed DNA sample taken from a firearm.
- Trinity DNA Solutions (lab) tested a known sample from Barton and an unknown mixed sample from the gun; lab analyst Candy Zuleger identified Barton as the “major contributor” of the mixed sample and computed a match statistic (1 in ~41 million).
- Barton conceded PCR/STR testing itself is routine but argued (1) the gun sample was a multi-person mixture (at least three donors) and (2) the lab lacked validated methods to identify a major contributor in three+-person mixtures and thus conclusions were unreliable (also asserted low-copy-number/stochastic issues).
- The Magistrate Judge held evidentiary hearings, found both experts qualified, and recommended denial of Barton’s motion — concluding the challenges went to weight, not admissibility, under Daubert/Fed. R. Evid. 702.
- The District Court reviewed Barton’s specific objections de novo, adopted the Magistrate Judge’s Report & Recommendation, overruled Barton’s objections, and denied the motion to exclude DNA evidence and testimony.
Issues
| Issue | Plaintiff's Argument | Defendant's Argument | Held |
|---|---|---|---|
| Admissibility of DNA expert testimony under Daubert / Fed. R. Evid. 702 | Govt: PCR/STR methods are routine, validated, generally accepted; methodological disputes go to weight | Barton: Specific conclusions (major-contributor call and stats) are not supported by sufficient facts/methodology and thus are unreliable | Court: Admit testimony; challenges to interpretation/validation go to weight, not admissibility |
| Reliability of applying lab validation (two-person) to three+-person mixtures | Govt: Trinity’s procedures and manufacturer validation, plus lab auditing, support use on real mixtures | Barton: Lab lacked validation for three+ person mixtures; extrapolation is scientifically unsupported | Court: Daubert does not require testing every conceivable use; lab procedures and conservative interpretation suffice for admissibility |
| Low copy number (LCN) / stochastic effects threatening reliability | Govt: Testing performed was PCR/STR (not LCN) and lab employed conservative methods to address potential dropout | Barton: Sample showed stochastic effects and possible allele drop-out/drop-in; results thus unreliable for major-contributor determination | Court: Trinity accounted for stochastic risks (used only 10 conservative loci and modified random match probability), which favored defendant; remaining disputes go to cross-examination/weight |
| Whether case law (e.g., McCluskey) required exclusion of LCN-style results | Barton: McCluskey supports excluding unreliable LCN results | Govt: Morgan and other authority more persuasive; PCR/STR generally admissible | Court: Relied on authorities permitting admission where methodology and lab controls exist; McCluskey not controlling, admission proper here |
Key Cases Cited
- Daubert v. Merrell Dow Pharm., 509 U.S. 579 (court acts as gatekeeper for scientific expert testimony)
- Kumho Tire Co. v. Carmichael, 526 U.S. 137 (Daubert gatekeeping applies to all expert testimony; abuse of discretion standard)
- McCorvey v. Baxter Healthcare Corp., 298 F.3d 1253 (11th Cir.) (proponent bears burden to show expert admissibility)
- Cook ex rel. Estate of Tessier v. Sheriff of Monroe County, 402 F.3d 1092 (11th Cir.) (party offering expert must establish qualification, reliability, helpfulness)
- Quiet Tech. DC-8 v. Hurel-Dubois UK Ltd., 326 F.3d 1333 (11th Cir.) (failure to account for allegedly relevant data is a matter of weight, not admissibility)
- U.S. v. Morgan, 53 F. Supp. 3d 732 (S.D.N.Y.) (PCR/STR methodology admission; challenges to specific procedures go to weight)