Impeaching an Expert Witness
Impeachment of an expert witness is the process of calling into question the credibility of the expert during cross-examination. According to the United State Federal Rules of Evidence, any party may attack the credibility of any witness (including an expert witness) during a trial.
Adequate preparation before the trial begins is essential for the successful impeachment of an expert witness. Such preparation involves becoming familiar with the expert's credentials as well as the subject matter of the cross-examination.
Lack of qualification is an initial challenge to any expert. Does this expert possess such specialized knowledge of the subject of his or her testimony that the court should declare this witness to be an "expert"? This is where it pays to spend significant time scrutinizing the expert's credentials.
Bias is one of the most common strategies for impeaching a witness at trial. This involves demonstrating that the witness is motivated in his testimony by personal gain - actual payment for testifying in that particular case or the hope that testimony in this case will lead to more business as an expert witness. Repeatedly testifying for the same side during trial is also sometimes grounds for impeachment because of bias.
Inconsistency is another reason for impeachment, and is generally the easiest to prove. If the expert witness has previously made two or more conflicting statements, or if prior testimony is in conflict with the testimony being offered during the current proceedings, a strong case for impeachment due to inconsistency can be made. Previous statements, such as those on affidavits, sworn statements, or previous depositions, should always be thoroughly reviewed prior to the beginning of testimony by an expert witness. Contradictions or inconsistencies made during the current testimony can also be used as grounds for impeachment.
Character of the expert witness can be called into question during cross-examination in order to prove justification for impeachment. If the witness has a reputation for dishonesty, or has committed a crime involving dishonesty, such as fraud, embezzlement, or perjury, a case for poor character can be made. This can go a long way toward convincing the court and jury that the testimony of the expert witness is not credible. Specific examples of prior dishonest acts or crimes are not admissible unless the witness admits to them while on the stand.
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