An Expert Witness Defined: A Beginner’s Guide

An Expert Witness Defined: A Beginner’s Guide

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It is difficult to imagine anything simpler than the definition of an expert witness – someone who can help the jury understand something, some aspect of the factual dispute, or possibly even an ultimate fact that the jury must decide on.

California Evidence Code §720 defines an expert as a person qualified to testify based on “special knowledge, skill, experience, training, or education . . .”

The goal is to identify the expert who will help you communicate to the jury some special information, which is beyond the reach of a lay witness. It is important to find a person with the particular qualities, background, experience, qualifications, integrity, and demeanor/personality that will best impact your jurors.

You can generally categorize experts in three groupings:


  • The hands-on expert, with some focus of his expertise, such as an engineer or geologist;
  • Paid consultants, offering testimony on your behalf based in their field of expertise;
  • And finally the expert who is a professional witness.

Once you’ve picked your expert, it is important to know your strategy and the path you want your expert to travel and to prepare your expert to be effective in front of the court.

  • You’ll want to illuminate the special knowledge, skill, experience, training, or qualifications of your proposed expert.
  • Set up your expert’s opinion, and remember to identify the information she has relied on in reaching that opinion.
  • Take the expert through her contradiction of the other party’s expert; you want your jury to believe your expert and doubt, if not completely dismiss, the other party’s.

Preparing an expert witness for court in support of your case must be a thorough process. In conclusion, prepare, prepare, and prepare. Use your meetings with your expert to prepare you for court. Do practice examinations with your expert, with her acting as your expert, and then theirs. Practice and watch, learn from, and follow good attorneys practicing the art of examination and trial. Ultimately, there is no substitute for experience and learning from the process. Preparing depositions, going on trial, and performing cross-examinations are the best means by which to gain experience in criminal law and employing the expert witness.

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