## Facts

- John Clyde Abel and two associates were indicted for a California bank robbery; the associates pleaded guilty and Abel went to trial.
- The government called accomplice Kurt Ehle, who testified implicating Abel.
- Abel sought to impeach Ehle through defense witness Robert Mills, who would testify that Ehle admitted he planned to falsely implicate Abel to obtain favorable treatment.
- The government disclosed it would rebut Mills by recalling Ehle to testify that Abel, Mills, and Ehle were members of a prison gang whose code required members to protect each other, including by perjury.
- On cross-examination, Mills denied knowledge of the gang.
- The district court permitted Ehle to testify about the gang’s existence and tenets as bearing on Mills’s potential bias.

## Issues

1. Whether evidence that a defense witness and the defendant share membership in a prison gang with a mutual-protection/perjury code is admissible under the Federal Rules of Evidence to show the witness’s bias.
2. Whether the evidence should nonetheless be excluded under Federal Rule of Evidence 403 because unfair prejudice substantially outweighs probative value, including prejudice to a non-testifying defendant by association.

## Decision

- The Supreme Court reversed the Ninth Circuit and reinstated the conviction.
- The Court held that the gang-membership evidence was relevant and admissible to impeach Mills for bias.
- The Court held that the district court did not abuse its discretion in concluding under Rule 403 that the evidence’s probative value was not substantially outweighed by unfair prejudice.
- The Court rejected a categorical rule barring bias evidence merely because it also reveals unsavory associations of a defendant who did not testify.

## Legal Principles

- The Federal Rules of Evidence permit impeachment for bias, consistent with pre-Rules common-law practice, even though “bias” is not expressly listed as a mode of impeachment.
- Evidence is relevant under Rule 401 if it has any tendency to make a consequential fact more or less probable; shared organizational membership can make a witness’s bias toward a party more probable.
- A witness’s and a party’s common membership in an organization may be probative of bias even without proof that the witness personally adopted all the organization’s tenets.
- Under Rule 403, trial courts have discretion to admit relevant bias evidence when its probative value is not substantially outweighed by the danger of unfair prejudice; the organization’s nature may affect both probative value and prejudice.
- Evidence offered to show a witness’s motive to lie is not rendered inadmissible solely because it incidentally reflects negatively on a non-testifying defendant.

## Conclusion

The Court held that evidence of shared prison-gang membership, including testimony about a gang code of mutual protection through perjury, was admissible to show a defense witness’s bias and was not excluded by Rule 403, even though it risked prejudicing the defendant by association.


United States v. Abel, 469 U.S. 45 (1984)