Impeachment is an attack upon the credibility of a witness and the trial court retains discretion to admit or exclude evidence offered for impeachment[i].

Under the Federal Rules of Evidence, the credibility of a witness may be attacked by any party, including the party calling the witness[ii].

Because the jury is the sole trier of fact and responsible for determining witness credibility and resolving conflicts in testimony, courts have held that jurors should be given every opportunity to hear impeachment evidence that may undermine a witness’s credibility[iii].  The law prohibits impeachment of witnesses en masse and stipulates that each witness must be impeached individually and in a lawful manner. Likewise, the general rule is that a witness may not be impeached before rendering testimony at trial.

The trial court decides the mode of impeachment of a witness.  Impeachment is accomplished by such methods as showing the existence of bias, a prior inconsistent statement, untruthful or dishonest character, or defective ability to observe, remember, or recount the matter about which the witness testifies.  A witness may be impeached on cross-examination or by other evidence contradicting the witness as to a material matter.  In some instances, rebuttal evidence may be used for impeachment purposes[iv].

The credibility of a witness is ordinarily tested by cross-examination.  However, expert testimony is also used to impeach the credibility of a witness.  The scope and extent of cross-examination of a witness depends on the discretion of the trial court.  The trial judge also has discretion to exclude questions designed only to impeach the witness, which would, if answered, tend to disparage third persons not connected with the case.

Courts have held that the cross-examiner should be accorded wide latitude in attempting to elicit facts which would tend to impeach or contradict testimony given on direct examination[v].

Any person offered as a witness is subject to impeachment[vi].  A party testifying in his/her own behalf in a civil action is subject to impeachment.  However, a party cannot ask a witness a question in order to later impeach the witness.  In criminal cases, both the witnesses for the prosecution and those for the defendant, including the accused when s/he takes the witness stand in his/her own behalf, may be impeached.  A defendant who elects to testify may be cross-examined on collateral matters bearing upon his/her credibility, the same as any other witness[vii].

Grounds for Impeachment

Mental impairment may be a proper subject of impeachment if it is shown that that factor affects the witness’ capacity to perceive, remember, and articulate correctly.

This is permissible even though the witness may not be mentally incompetent to testify[viii].  Intoxication, habitual drunkenness, or drug addiction may affect a witness’ testimonial credibility.

Courts have taken different standpoints regarding the issue whether evidence of drug use is admissible to show a general lack of veracity on the part of a witness.  Most courts are of the opinion that evidence of drug use proffered to show a lack of veracity is inadmissible[ix].

The usual method of impeachment is to demonstrate that a witness harbors bias or prejudice toward one of the parties.  Alternatively a showing of a personal interest in the outcome of the trial which can be expected to color his/ her testimony and undermine its reliability is sufficient.  The fact that the circumstances which show the bias of a witness may also incidentally prejudice the jury against the party in whose favor the witness is testifying is immaterial and is not a reason for the exclusion of the evidence.  A witness is deemed to be biased if the witness has a friendly or hostile feeling toward a party and a witness is interested if the witness has a stake in the outcome of the case[x].

Impeachment of a witness for motive, bias, and interest may be accomplished by the introduction of extrinsic evidence[xi].

[i] People v. Brown, 31 Cal. 4th 518 (Cal. 2003).

[ii] Fed. R. Evid. 607.

[iii] Atkinson v. State, 778 A.2d 1058 (Del. 2001).

[iv] People v. Harris, 98 N.Y.2d 452 (N.Y. 2002).

[v] U.S. v. Crumley, 565 F.2d 945 (5th Cir. 1978), Myrick v. State, 508 So. 2d 1215 (Ala. Crim. App. 1987).

[vi] State v. Gabriel, 450 So. 2d 611 (La. 1984).

[vii] State v. Culkin, 97 Haw. 206 (Haw. 2001).

[viii] Commonwealth v. Caine, 366 Mass. 366 (Mass. 1974).

[ix] United States v. Bertram, 805 F.2d 1524 (11th Cir. Ga. 1986).

[x] State v. Barfield, 79 Ore. App. 688 (Or. Ct. App. 1986).

[xi] State v. Ferguson, 260 Conn. 339 (Conn. 2002).