In a court trial, the witnesses in a case are usually people who are involved in the case in some way or who have firsthand knowledge of it, e.g., they were present when something happened and can attest to what they saw and heard.
An expert witness is an exception to that rule: Someone who testifies not about what happened in the case but about background information relevant to it.
What Does an Expert Witness Do?
An expert witness testifies about information that is relevant to the case based on specialized training, education, or experience in a particular field. For example, a financial expert witness can testify about money matters, a doctor can give a medical diagnosis, etc.
What Special Rules Apply to Expert Witnesses?
Generally, witnesses testifying in court have to stick to facts and observations. They are not allowed to give opinions or make analyses. An exception is made for expert witnesses. Their job is to analyze evidence and draw conclusions based on their findings, then share their professional opinions with the jury.
What Role Does an Expert Witness Play in a Jury Trial?
To render a fair verdict, a jury sometimes needs specialized background information that the average person does not have. An expert witness gives context, providing the necessary information that the jury needs to reach a decision.
If a person who already has expert knowledge in a field relevant to the case is called for jury duty, he or she may not be asked to sit on the jury. The court does not want jury members to make decisions based on prior knowledge or past experience. The system of justice depends on juries making decisions solely on the facts presented in court.
A potential juror will be asked to disclose any knowledge or past experience he or she has with matters related to the case. If he or she fails to disclose the information prior to the trial, it could call the validity of the decision into question.
