Cross-examination goals essentially boil down to 1) developing facts which support your case, 2) harm the defense case and 3) impair credibility. You must carefully analyze the first two goals before you decide to impair the credibility of a witness.
When the witness has not harmed your case, there should be no reason to cross-examine, let alone challenge credibility. Although the jury anticipates a thorough cross and looks forward to it, you must quickly resist the temptation. Unnecessary cross-examination opens the door to a witness suddenly surprising you with something harmful. It also opens up further redirect and the chance for something harmful to develop.
When the witness has harmed your case on direct examination, you should first consider cross-examination to elicit some helpful facts. This would entail a series of simple, short statements that the witness must agree upon. Such cross-examination may address corroboration of a time line, the weather at the time of the occurrence, persons present at the scene, laying foundation for documentary evidence, etc. While you do not want to give the harmful witness any more importance to the case than necessary, you may have to when the witness is the only source for the evidence.
If you determine that you can successfully challenge a harmful witness credibility (impeachment) you must first understand that the impeachment does not necessarily mean that all of the witness’ testimony will be determined to be unreliable. Rather, as stated in California Civil Jury Instruction 107, the jury remains the sole judge of witness believability:
Sometimes a witness may say something that is not consistent with something else he or she said. Sometimes different witnesses will give different versions of what happened. People often forget things or make mistakes in what they remember. Also, two people may see the same event but remember it differently. You may consider these differences, but do not decide that testimony is untrue just because it differs from other testimony.
However, if you decide that a witness has deliberately testified untruthfully about something important, you may choose not to believe anything that witness said. On the other hand, if you think the witness testified untruthfully about some things but told the truth about others, you may accept the part you think is true and ignore the rest.”
The three most often used methods to impair witness credibility include prior inconsistent statements, character evidence and case-specific impeachment.
NEXT: Witness Credibility and Prior Inconsistent Statements