## Facts

- Border Patrol agents encountered a group of undocumented migrants on Otay Mountain near the U.S.–Mexico border.
- The government alleged Gabriel Sanchez-Lima escaped during an initial attempt to apprehend the group, later struck an agent with a rock, and attempted to take another agent’s gun during the struggle.
- Sanchez-Lima contended agents used excessive force early in the encounter and then lied to conceal it.
- The defense asserted Sanchez-Lima acted in self-defense when approached through brush by an agent who allegedly did not identify himself, based on a claimed reasonable fear of being beaten again.
- Multiple migrant eyewitnesses were apprehended that night; several were deported shortly after the incident.
- Before trial, the defense sought to use sworn videotaped eyewitness statements from deported witnesses and moved to take their depositions in Mexico; the district court refused.
- At trial, a Border Patrol agent was permitted to offer an opinion that another testifying agent was telling the truth.

## Issues

1. Whether the district court erred by admitting opinion testimony effectively vouching for the truthfulness of another witness’s trial testimony.
2. Whether, in a prosecution under 18 U.S.C. § 111 where self-defense is raised, the jury must be instructed that the government bears the burden to disprove self-defense beyond a reasonable doubt.
3. Whether the exclusion of sworn videotaped statements and the denial of depositions of deported eyewitnesses improperly limited the defense and contributed to an unfair trial.

## Decision

- The Ninth Circuit reversed the conviction and remanded for a new trial.
- The court held it was error to admit testimony that directly endorsed another witness’s truthfulness, because it invaded the jury’s role in resolving credibility disputes.
- The court held it was error to omit an instruction that, once self-defense is at issue, the prosecution must disprove self-defense beyond a reasonable doubt.
- The handling of deported eyewitnesses was addressed in the court’s assessment of prejudice, given the centrality of credibility and the defense theory.

## Legal Principles

- A witness generally may not testify that another witness’s specific testimony is true; such credibility opinions are inadmissible except within the limited scope of character-for-truthfulness evidence permitted by Fed. R. Evid. 608.
- Improper credibility vouching is especially prejudicial where the case turns on competing accounts and the jury must decide which witnesses to believe.
- In a federal prosecution for assault on a federal officer under 18 U.S.C. § 111, once the defendant produces some evidence of self-defense, the government must prove beyond a reasonable doubt that the defendant did not act in self-defense.
- Failure to clearly instruct on the government’s burden to disprove self-defense is reversible error when self-defense is supported by evidence and materially contested.

## Conclusion

The Ninth Circuit ordered a new trial because the jury heard improper opinion testimony endorsing an agent’s credibility and was not instructed that the government had to disprove self-defense beyond a reasonable doubt, errors that were material in a case hinging on witness credibility and the defendant’s claimed justification.


United States v. Sanchez-Lima, 161 F.3d 545 (9th Cir. 1998)