Witness impeachment

Witness impeachment, in the law of evidence, is the process of calling into question the credibility of an individual who is testifying in a trial. There are a number of ways that a witness may properly be impeached, and several ways that, although effective, are prohibited except under special circumstances.

Methods of impeachment

A party may be impeached through introducing evidence of any of the following (remembered via the mnemonic BICCC):
* Bias--The witness is biased against one party or in favor of the other. The witness has a personal interest in the outcome of the case. A classic example is a witness for the prosecution who is awaiting sentencing. He's more likely to be pro-prosecution in hopes of better treatment. The proper way to handle this is first to question the witness to see if he will admit to the bias. If not, then the cross-examiner may bring in other witnesses to expose the bias.
* Inconsistent Statement--The witness has made two or more conflicting statements. By exposing his conflicting statements, you reduce his credibility.
* Character Show that the witness has a community-recognized reputation for dishonesty. Specific examples are inadmissiblendash unless the witness admits them himself under cross-examinationndash but to present witnesses who can attest to the witness's character is helpful. This might seem tedious, especially when it is realized that a character witness against the principal witness may himself be impeached the same way, but normally witnesses are total unknowns to jurors, and people with reputations in their community for being total fabricators do show up in court from time to time. Coupled with character are prior criminal acts by the witness. This is handled in one of three ways:
** If the witness has committed any crime involving dishonesty (i.e. larceny-by-trick, embezzlement, fraud, etc.) then the prior conviction is admissible under every circumstance.
** If the witness is the criminal defendant, a felony conviction (i.e., conviction of a crime that is punishable of at least one year in prison) is admissible if the judge determines that the probative value outweighs the potential for prejudice.
** If the witness is not the criminal defendant, a felony conviction is admissible unless the judge determines that its prejudical nature "substantially" outweighs its probativity.
** Stale felonies, that is, felonies where the witness was released at least ten years ago (or was found guilty ten years ago if no incarceration) are admissible only if the probative value substantially outweighs its prejudice.
* Competency Basically show that the witness was unable to sense what he claimed to have (i.e., could not see from where he was, etc.) or that he lacked the requisite mental capacity. Older common law would exclude an incompetent witness from testifying. Modern rules, and the Federal Rules of Evidence allow the witness on the stand (in most cases) considering competence but one of many factors juries are to consider when determining credibility of the witness.
* Contradiction This occurs when the witness is induced to contradict his own testimony during the present proceeding. This differs from inconsistent statements, above. Inconsistent statements involve statements made out-of-court (cf. hearsay) or in prior proceedings. Contradiction involves the witness saying two different things while presently testifying.

Another form of impeachment by contradiction has a subtle effect on the order in which the attorneys present their evidence. When a defense attorney calls a witness who testifies about what happened, this gives the opposing attorney the opportunity to present evidence contradicting that witness. Had impeachment by contradiction not been allowed by the rules of evidence, the second attorney would have been barred from presenting the contradicting evidence because he already had his one (and only) chance to prove the facts of the case as he claims them to be. But since his opponent put on a witness, this "opens the door" to him to strengthen his case by going again with more proof of what happened: the only legal excuse for this re-hash of his claim is that he is impeaching by contradiction his opponent's witness. Another use of impeachment by contradiction can be explained negatively: while an attorney cannot contradict an opponent's witness on a trivial ("collateral") fact, like the color of the hat she testified she was wearing on the day she witnessed the accident, on more important matters normally excluded by the rules of relevance, contradiction may be allowed. Thus, a witness might not normally be permitted to testify she is a safe driver, and the opponent cannot normally prove she is in general an unsafe driver, but should the witness nonetheless happen to testify she is a safe driver (say because no objection was made to the question), her opponent can now contradict her by eliciting on cross-examination that she has been involved in several accidents. Had contradiction impeachment not be permitted, then the unsafe character of the witness would have been barred by the rules of evidence. This impeachment-by-contradiction evidence is admitted solely to impeach, that is, cannot be used to prove anything about the events being litigated, but can only be used to discredit the witness's credibility. The theory is when a witness can be contradicted, that should be taken into account in determining the reliability of the witness. Hence, the jury is instructed by the judge "do not use [the impeachment evidence} as proof of any facts, but only to consider whether the witness in question should be believed." All experienced courtroom observers agree that jurors will have great difficulty understanding this distinction, known as "limited admissibility" or "admissibility for a limited purpose". Even more unlikely is the prospect that a juror who understands the instruction will be psychologically capable of obeying it. The only practical impact of this limited admissibility is that the evidence cannot be used to prop up a weak case that would otherwise be dismissed by the court for insufficient evidence--because it was admitted only for the impeachment of a witness.

Who may impeach?

Under the common law of England, a party could not impeach his own witness unless one of four special circumstances was met. This was due to the "Voucher Rule", which required that the proponent of the witness "vouche" for the truthfulness of the witness. The special circumstances were:
#If the witness was an "adverse party" (e.g. if the plaintiff called the defendant to the stand, or vice-versa).
#If the witness was "hostile" (e.g. refused to cooperate).
#If the witness was one that the party was required by law to call as a witness.
#If the witness surprised the party who called him by giving damaging testimony against that party.This rule has been eliminated in many jurisdications. Under the United States' Federal Rules of Evidence, (F.R.E. 607), any party may attack the credibility of any witness.

Bolstering and Rehabilitating

The general rule is that the proponent of a witness may not attempt to build up the witnesses credibility prior to his being impeached. The rationale is that the witness is presumed trustworthy. It also speeds proceedings by not spending time bolstering when the other side may not even impeach the witness.

In order to rehabilitate a witness, the proponent is confined to using the same techniques used by the opponent to impeach the witness. That is, if the opponent impeached via bias, then rehabilitation is limited to negating the claim of bias. If the opponent brought in a rebuttal witness who testified to the character of principal witness as that of a liar, rehabilitation is limited to a character witness who testifies principal witness is a truthful person. (Note: this is a different consideration from the ever-present right to cross-examine any witness, including character witnesses).

If the opponent showed 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. The jury is left with two pre-trial statements that are inconsistent with each other, but only one is inconsistent with the testimony, and both were made before the witness was allegedly gotten to, so there might be softening of the accusation that the testimony flows from, e.g., a bribe. And there is always a case for allowing a prior consistent statement made at any time before trial to help explain away what is arguably only a seemingly inconsistent statement that is subject to interpretation because, e.g., it was lifted out of explanatory context.