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 who is testifying in a trial. The Federal Rules of Evidence ("F.R.E.") contain the rules governing impeachment in federal courts.

Parties who may impeach

Under the common law of England, a party could not impeach her 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 "vouch" for the truthfulness of the witness. The special circumstances were:

1. If the witness was an adverse party (e.g. if the plaintiff called the defendant to the stand, or vice-versa).
2. If the witness was hostile (e.g. refused to cooperate).
3. If the witness was one that the party was required by law to call as a witness.
4. If the witness surprised the party who called him by giving damaging testimony against that party.

This rule has been eliminated in many jurisdictions. Under the United States' Federal Rules of Evidence, F.R.E. 607 permits any party to attack the credibility of any witness.

Methods of impeachment

In the United States, a party has the option of discrediting a witness through impeachment by cross-examining the witness about facts which reflect poorly on the witness' credibility, or—in some cases—by introducing extrinsic evidence that reflects negatively on the witness' truthfulness or knowledge.

Impeachment categories

A party may impeach a witness in the United States by introducing evidence of any of the following (remembered via the mnemonic BICCC):

Bias
Courts permit parties to cross-examine a witness in order to impeach that witness based on his or her demonstration of bias. Witness bias may be catalyzed by any number of circumstances, ranging from the witness' blood relationship to a party to her financial stake in the outcome of the litigation. A majority of U.S. jurisdictions require a cross-examiner to lay a foundation before using extrinsic evidence to demonstrate bias for impeachment purposes. Although F.R.E. 610 provides that evidence of a witness' "religious beliefs or opinions is not admissible to attack or support the witness’s credibility," an inquiry into the witness' religious beliefs or opinions for the purpose of showing interest or bias because of them is not within the rule's prohibition.

Inconsistent statement
F.R.E. 613 provides that a witness who gives present trial testimony inconsistent with his or her previously-made statements may be impeached by attorneys for either party, including the party that called the witness, through cross-examination. The Federal Rules do not require a cross-examining attorney seeking to impeach a witness for prior inconsistent statement purposes to first disclose to the witness any extrinsic evidence the attorney possesses regarding the witness' prior inconsistent statement, though the adverse party must be shown such extrinsic evidence, if she requests it.

Prior inconsistent statements are not barred by the hearsay rule, and are thus admissible for the truth of the matter asserted, so long as they meet the requirements of F.R.E. 801(d)(1)

• Note that under California Evidence Code ("CEC") §§769, 770, and 1235, prior inconsistent statements may be used for both impeachment and substantive use purposes. Furthermore, the statement need not have made under oath at a formal proceeding to be used for substantive purposes.
  

Character
A majority of U.S. jurisdictions permit parties to impeach witnesses by demonstrating their "bad" character regarding truthfulness. Under the Federal Rules a party may demonstrate a witness' "bad" character through reputation or opinion testimony.

Additionally, a party may impeach a witness for "bad" character by introducing evidence of the witness' prior conviction of a crime, subject to a series of rules laid out in F.R.E. 609(a). If the witness' prior conviction was for a crime involving dishonesty or false statement, evidence of that crime is admissible for impeachment purposes regardless of whether the crime was a misdemeanor or a felony. If the witness' prior conviction was for a crime not involving dishonesty or false statement, evidence of the conviction is only admissible for impeachment if the crime was a felony—misdemeanors are inadmissible. Furthermore, if the cross-examining party seeks to introduce evidence of a felony not involving dishonesty or false statement, its success in impeaching the defendant will depend on whether the witness is the defendant or one other than the defendant. If the witness is defendant, the burden is on the prosecution to show that the probative value of the impeachment—i.e. demonstrating the defendant witness' propensity to lie—outweighs the danger of unfair prejudice to the defendant. 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. Finally, if a conviction is more than ten years old, its probative value is deemed evaporated, and it is therefore inadmissible under F.R.E. 609(b)

A party may impeach a witness for character by cross-examining the witness—but not by introducing extrinsic evidence—about specific instances of prior misconduct, often called "prior bad acts," as long as the questions relate to the witness' own character for truthfulness (or untruthfulness) or to the character for untruthfulness of a previous witness that the current witness has testified about before.

• Note that under California Evidence Code ("CEC") §787, a party may not use either cross-examination or extrinsic evidence to impeach a witness' by showing specific instances of prior misconduct—in civil cases. Proposition 8, the Victims' Bill of Rights passed by CA voters 1982, permits parties to use both cross-examination and extrinsic evidence about specific instances of prior misconduct in criminal cases to impeach a witness.
  

Competency
The witness was unable to sense what he claimed to have (such as he could not see from where he was) or that he lacked the requisite mental capacity. Older common law would exclude an incompetent witness from testifying. Modern rules, such as the Federal Rules of Evidence, allow the witness on the stand (in most cases) considering competence, but one of many factors that juries are to consider when determining credibility of the witness.

Contradiction
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 (hearsay) or in prior proceedings. Contradiction involves the witness saying two different things in the same testimony.

An attorney impeaching a witness during a mock trial competition

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 rehash 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, but 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 been 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: it cannot be used to prove anything about the events being litigated but only to discredit the witness's credibility. The theory is that when a witness can be contradicted, it 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.

Bolstering and Rehabilitating

The general rule is that the proponent of a witness may not attempt to build up the witness's 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 that this is a different consideration from the ever-present right to cross-examine any witness, including character witnesses.

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. 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 such as a bribe. Also, 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, for example, it was lifted out of the context that would explain the statement.