Bias is a term used in the common law of evidence to describe the relationship between a party and a witness which might lead the witness to slant, unconsciously or otherwise, his testimony in favor of or against a party. Bias may be induced by a witness' like, dislike, or fear of a party, or by the witness' self-interest. Proof of bias is almost always relevant because the jury, as finder of fact and weigher of credibility, has historically been entitled to assess all evidence which might bear on the accuracy and truth of a witness' testimony. The common law of evidence allows the showing of bias by extrinsic evidence, while requiring the cross-examiner to take the answer of the witness with respect to less favored forms of impeachment.
The defendant and two others were charged with bank robbery. The two co-defendants pleaded guilty, and one agreed to testify against defendant. The defendant countered with a witness to impeach the testimony of the co-defendant. The co-defendant was then permitted to testify regarding the witness's membership in a prison gang that would commit perjury on its members' behalf. The trial court admitted the evidence, and defendant was convicted. The defendant sought review and argued that the rebuttal testimony lacked probative value and did not outweigh the prejudicial effect. The appellate court reversed his conviction and found that the testimony prejudiced defendant because it implicated him as gang member and had the effect of impeachment, even though he did not take the stand.
Was the prejudicial testimony which implicated the defendant as a gang member permissible and sufficient to warrant admission?
The Court held that the testimony was sufficiently probative of the defense witness possible bias toward the defendant to warrant its admission into evidence, regardless of whether the testimony was inadmissible under Rule 608(b) as extrinsic evidence of the witness' past conduct bearing on his veracity. Furthermore, it added that the impeachment of a witness for bias is permissible under the Federal Rules of Evidence.