Impeaching Expert Witnesses

Lawyers know that the grounds for impeaching an expert witness are different from those of impeaching an ordinary witness. For the impeachment of ordinary witnesses, the opponent’s lawyer may invoke either bias of the witness, lack of personal knowledge, lack of competence, character, credibility, or inconsistent statements.

Today, David Serna discusses the grounds that effectively impeach an expert witness.

1. Lack of expertise and qualifications

Lawyers, before agreeing to accept an opponent’s expert witness, must object if the expert witness lacks the experience or technical knowledge to which he will be testifying. Many lawyers make the mistake of passively agreeing to the presentation of an expert even when he or she is not a declared expert in the field.

To prepare for the objection, the lawyer must, in advance of trial, research on the background of the expert witness. To challenge the expertise during pre-trial, the lawyer must file a motion in limine before the court, asking that such witness be precluded. In the motion, the legal basis for precluding the witness must be given.

2. Prior inconsistent statements

Like an ordinary witness, an expert witness may be impeached based on this ground. Reports, transcripts, documents, or signed statements given by the expert witness at a prior time may be used against him if they are inconsistent with his or her testimony.

However, the lawyer must not misquote the expert witness. In using excerpts, he must not summarize and take the statement out of context. Misunderstanding the context will only create a disadvantage to his case as this may seem like he is merely putting words into the witness’ mouth.

3. Articles authored by the expert

Lawyers may object using articles written by the expert if they are inconsistent with his or her testimony. The lawyer must first let the expert witness identify the article or publication. David Serna advises that lawyers present a copy of the article to the jury. After the witness has identified the article, the lawyer must not ask questions regarding the article. It is best to present the conclusions to the jury during the closing statement.

David Serna is a defense attorney based in New Mexico. His topics cover prosecution, trial, criminal law, and criminal defense.