United States v. Enrique Valencia-Lopez, 971 F.3d 891

Background

Valencia-Lopez, a commercial truck driver, crossed from Mexico into Arizona with bell peppers; inspectors found ~6,230 kg of marijuana hidden in the load.
Valencia-Lopez testified he was kidnapped in Mexico, his truck briefly taken, then returned by armed men who ordered him to continue or they would kill him and his family; he asserted a duress defense and received a duress jury instruction.
The government called ICE/Homeland Security Investigations Supervisory Agent Matthew Hall as an expert; Hall testified (without a demonstrated methodology) that the likelihood a cartel would entrust a large load to a coerced commercial driver was "almost nil, almost none."
The district court denied Valencia-Lopez’s requests for a Daubert hearing and for voir dire, qualified Agent Hall as an expert, but made no explicit Rule 702 reliability findings.
On appeal the Ninth Circuit held the district court abdicated its Daubert/Kumho gatekeeping duty and that the government failed to establish a reliable basis for Hall’s near-zero-probability opinion.
The court concluded the error was not harmless because Hall’s testimony directly undercut the duress defense, vacated the convictions, and remanded for a new trial.

Issues

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether the district court satisfied its Daubert/Rule 702 gatekeeping duty before admitting Agent Hall's testimony	District court abused discretion; it made no explicit reliability findings and denied Daubert hearing/voir dire	Trial court permissibly relied on Hall's experience; voir dire/hearing not required; objections went to weight	Abuse of discretion: court abdicated gatekeeping by failing to make an explicit reliability determination and by denying voir dire/hearing
Whether Agent Hall's "almost nil" opinion was supported by reliable principles or methods	Hall offered no methodology or link between experience and his near-zero probability conclusion	Hall's extensive law-enforcement experience, interviews, case reviews and prior expert work suffice to show reliability	Not reliable: government failed to establish reliable basis for the specific "almost nil" opinion
Whether admission of Hall's testimony was harmless error	Hall's opinion struck at the core of duress defense and undermined defendant and defense expert; prejudice presumed	Jury could reject Valencia-Lopez's story regardless; defense had its own expert (Dr. Chalk)	Not harmless: error likely affected substantial rights; convictions vacated and remanded for new trial
Whether Hall's testimony violated Rule 704(b) (testimony on ultimate issue)	(raised on appeal) Hall improperly opined on a defense element (duress)	Court: 704(b) bars opinions about a defendant's mental state only when testimony necessarily implies the ultimate conclusion; Hall's opinion did not cross that line	If otherwise admissible, Hall's testimony would not have violated Rule 704(b); court did not reach exclusion on that ground

Key Cases Cited

Daubert v. Merrell Dow Pharm., 509 U.S. 579 (U.S. 1993) (established federal gatekeeping standard for expert testimony)
Kumho Tire Co. v. Carmichael, 526 U.S. 137 (U.S. 1999) (Daubert gatekeeping applies to non‑scientific expert testimony)
United States v. Ruvalcaba‑Garcia, 923 F.3d 1183 (9th Cir. 2019) (district court must make explicit reliability finding or record must show one)
Estate of Barabin v. AstenJohnson, Inc., 740 F.3d 457 (9th Cir. 2014) (trial court has broad latitude but must assess reliability and cannot abdicate gatekeeping)
United States v. Hinkson, 585 F.3d 1247 (9th Cir. 2009) (abuse of discretion and review framework for evidentiary rulings)
United States v. Hermanek, 289 F.3d 1076 (9th Cir. 2002) (expert must explain methods and tie them to conclusions)
Gen. Elec. Co. v. Joiner, 522 U.S. 136 (U.S. 1997) (requires a reliable bridge between data and expert conclusions)
United States v. Alatorre, 222 F.3d 1098 (9th Cir. 2000) (voir dire may satisfy gatekeeping when used to test expert reliability)