Witness impeachment
Witness impeachment, in the law of evidence of the United States, is the process of calling into question the credibility of an individual testifying in a trial.
Under the common law of England, a party could not impeach its own witness unless one of four special circumstances was met.
Most US jurisdictions require a cross-examiner to lay a foundation before extrinsic evidence can be used to demonstrate bias for impeachment purposes.
[4] A party may impeach a witness by introducing those of his prior statements that are inconsistent with his current testimony at trial.
In a minority of jurisdictions that follow FRE 801, the prior inconsistent statement may be used not only to impeach but also as substantive evidence.
[5] The majority of US jurisdictions permit parties to impeach witnesses by demonstrating their "bad" character regarding truthfulness.
If the witness is a person other than the defendant, the evidence of the prior felony conviction for a crime not involving dishonesty or false statement is admissible unless the party objecting to the evidence succeeds in the more difficult task of proving that the probative value of the felony conviction is substantially outweighed by the danger of unfair prejudice to the defendant.
Proposition 8, the Victims Bill of Rights passed by in 1982, permits parties to use both cross-examination and extrinsic evidence about specific instances of prior misconduct in criminal cases to impeach a witness.
Another form of impeachment by contradiction has a subtle effect on the order in which the attorneys present their evidence.
An attorney cannot contradict an opponent's witness on a trivial ("collateral") fact like the color of the hat worn on the day she witnessed the accident, but on more important matters normally excluded by the rules of relevance, contradiction may be allowed.
Had contradiction impeachment not been permitted, the unsafe character of the witness would have been barred by the rules of evidence.
Suppose the defendant foolishly testifies on direct examination, "In fact, I've never possessed heroin in my life."
[16] Harris, in turn, led to a decision allowing similar impeachment by physical evidence that had been suppressed in the same case as having been seized from defendant in violation of his Fourth Amendment rights.
If the opponent shows that the witness made a prior inconsistent statement and implies that after that statement and prior to trial the witness was "gotten to" or otherwise developed a motive to lie in court, rehabilitation can be attempted by showing that the witness made a prior consistent statement (consistent with the testimony) before the alleged events that gave rise to the alleged motive to lie.
