Impeaching a witness is a common tactic used to weaken the evidence of an opponent. There are many ways to challenge the credibility of the testimony, discredit, or impeach a witness. Lawyers must bear in mind these grounds as they become relevant during the cross-examination. The goal is to give the jury a reason not to believe the testimony of such a witness.
Today, David Serna gives helpful advice on how to challenge the credibility of a witness based on lack of competency.
Federal Rule of Evidence 601: General Rule of Competency
The provision in the FRE gives a broad scope for the competency of a witness. The law presumes that every person is a competent witness. It is then up to lawyers to find restrictions to the competency of a witness.
Fact witnesses are generally considered competent; whereas opinion witnesses must be able to prove that they are qualified to give opinions. Qualifications are based on foundational evidence, which is subject to cross-examination.
David Serna stresses that lawyers must discern whether the opinion offered by the witness is exaggerated or whether the witness has overstated his or her qualifications. Lawyers must first examine the experience, educational background, and credentials of the expert witness.
Counsels usually get all-purpose expert witnesses to help their theory of the case. The opposing counsel must be mindful of whether the witness is an expert on the subject being testified about. During the cross-examination, the opposing counsel is tasked to limit the testimony of the witness to his or her area of expertise.
Should the counsel perceive that the witness is underqualified, he must attack the witness’ competency either by filing a motion to exclude the testimony or by exposing the witness’ disqualifications during the cross-examination. The lawyer may start asking questions involving the witness’ undergraduate degree or the work in which he or she is engaged.
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David Serna 