United States v. Medina-Copete, 757 F.3d 1092

Medina and Goxcon were convicted on drug trafficking charges arising from a stop on I-40 in New Mexico and a secret methamphetamine stash found in a vehicle they borrowed.
During the stop, a law enforcement expert testified about Santa Muerte and connected iconography to drug trafficking, prompting defense challenges.
A DEA interviewing process and subsequent trial involved experts Almonte (on narco saints) and Hella (drug-organization MO), with disputed qualifications.
The district court admitted Almonte’s testimony under Rule 702, deeming it reliable and helpful though it relied on questionable data and methodology.
The appeals court vacated the convictions on counts 1–3 and remanded for a new trial, finding Almonte’s testimony prejudicial and not properly reliable under Daubert/Kumho.
The court also addressed the admissibility of Hella’s testimony and the handling of Rule 704(b) objections, but left those issues for potential retrial; Medina’s sufficiency challenge was considered as to knowledge of meth presence.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Admissibility of Almonte’s Santa Muerte testimony	Medina/Goxcon argue Rule 702/Daubert gatekeeping failed	State relied on precedent that narco-saint evidence is probative	Abused proper gatekeeping; testimony inadmissible under Rule 702; convictions on counts 1–3 vacated and remanded
Whether Santa Muerte testimony fits as a 'tool of the trade'	Testimony improperly linked iconography to drug distribution	Testimony viewed as relevant to trafficking practices	Testimony not properly connected to a legitimate 'tool of the trade'; district court erred in admitting it
Whether Almonte’s testimony was harmless error	Error did not affect substantial rights	Error was harmless in light of other evidence	Not harmless; grave doubt about outcome; convictions vacated (counts 1–3) and remanded
Whether Hella’s Rule 704(b) analysis was proper	Hella’s opinion on defendants’ mental state improperly invaded jury determination	Court properly allowed experiential testimony	Rule 704(b) objections not dispositive here; addressed but not central to the reversal; remand controls
Sufficiency of evidence as to Medina’s knowledge of drugs	Evidence suffices to prove knowledge	Insufficient link to knowledge given language barriers and conflicting accounts	Evidence viewed in most favorable light found sufficient to convict; however, convictions vacated on counts 1–3 due to reversible error not harmless

Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (Sup. Ct. 1993) (gatekeeping reliability standard for expert testimony)
Kumho Tire Co. v. Carmichael, 526 U.S. 137 (Sup. Ct. 1999) (extension of Daubert to non-scientific expert testimony; reliability applies broadly)
United States v. McDonald, 933 F.2d 1519 (10th Cir. 1991) (tools-of-the-trade paradigm; relevance of items related to drug trade)
United States v. Robinson, 978 F.2d 1554 (10th Cir. 1992) (permission for expert testimony on gang affiliation as related to conspiracy)
United States v. Garza, 566 F.3d 1194 (10th Cir. 2009) (Daubert reliability may be tailored to case specifics)