United States v. Robert William Barton, 909 F.3d 1323

Defendant Robert Barton was convicted of being a felon in possession of a firearm (18 U.S.C. § 922(g)) after police found a loaded .22 revolver with its serial number scratched off under the passenger seat of a car he was driving.
At arrest Barton confessed at the scene that the gun was his; he later again confessed to a jailhouse informant.
DNA testing of the firearm was performed by Trinity DNA Solutions; the analyst (Candy Zuleger) testified the major DNA profile on the gun matched Barton and had a population frequency of 1 in 41 million.
Barton moved to exclude the DNA testimony under Daubert, arguing the sample was a low-quantity three-person mixture, Trinity lacked validation for such mixtures, and peak-height/interpretation thresholds were inadequate.
A Daubert hearing with competing experts was held; the magistrate judge and district court denied exclusion, concluding methodology (PCR/STR and Trinity’s procedures) was generally reliable and the defense critiques went to weight, not admissibility.
On appeal the Eleventh Circuit affirmed: it declined to consider post-trial scientific guidelines/articles not in the trial record, found no abuse of discretion in admitting the DNA testimony, and held any error would have been harmless given overwhelming non-DNA evidence (confessions, corroborating witness testimony).

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether the district court abused its Daubert gatekeeping discretion in admitting expert DNA testimony from Trinity	Barton: DNA opinion unreliable because (1) sample was low-quantity (210 pg) raising stochastic effects; (2) the sample was a complex ≥3-person mixture and Trinity lacked validation studies for such mixtures; (3) Trinity’s peak-height/major-donor thresholds were inadequate	Government: PCR/STR methodology is generally reliable; Trinity followed accredited, audited procedures and validation guidance; contested aspects of interpretation go to weight and credibility for the jury	Admission affirmed; district court did not abuse discretion. Post-trial guidelines/articles not in the record were not considered on appeal. Any error would be harmless given overwhelming non-DNA evidence.

Daubert v. Merrell Dow Pharm., 509 U.S. 579 (establishing admissibility/w reliability framework for scientific expert testimony)
Kumho Tire Co. v. Carmichael, 526 U.S. 137 (gatekeeping standard applies to all expert testimony; abuse-of-discretion review)
United States v. Frazier, 387 F.3d 1244 (11th Cir.) (explaining Daubert factors and three-part Rule 702 inquiry)
Quiet Tech. DC-8 v. Hurel-Dubois UK Ltd., 326 F.3d 1333 (11th Cir.) (distinguishing admissibility from credibility; flaws in application typically go to weight and cross-examination)
Gen. Elec. Co. v. Joiner, 522 U.S. 136 (abuse-of-discretion is proper appellate standard for admissibility rulings)