Witness sworn in

What is an Expert Witness?

In law, there are two kinds of witnesses: witnesses of fact and expert witnesses. A witness of fact is usually someone who either saw an incident take place or was connected with the other witnesses in some way. An expert, on the other hand, is typically separate from the case and brings more scientific data to the case. What is an expert witness, and when do cases call for them? Let us explain.

Scientific Evidence

Court trials have specific rules for admitting evidence. Generally speaking, exhibits can only “enter evidence” when a witness is familiar with them. Some pieces of evidence, especially in cases involving forensics, are more obscure and require special attention.

An expert witness can identify these special exhibits and help add them into evidence. If the expert has worked with the exhibit while reviewing the case, they can also offer their opinion about the item and the scientific processes used to evaluate it.

Proper Opinion

Expert witnesses are subject to intense rules, beyond those of a witness of fact. An expert must first validate themselves as a witness through a series of background questions asked by the attorney. Once established, they can only discuss the evidence and processes used in the case. If they offer their opinion on something outside the scope of their research, an attorney might object.

Likewise, if a witness of fact gives their opinion on a scientific matter without proving themselves an expert, an attorney may object and have that opinion stricken from the stenographer’s report.

Cross-Examination

When an attorney has finished their initial questioning, the opposing attorney has a chance to “cross-examine.” In this, the attorney will ask questions that highlight the weaknesses of the evidence and the scientific processes. They will point out errors in methodology and attempt to debunk “voodoo science.”

Attorneys spend years learning how to address an expert witness and break down the evidence in a way that is simple to understand. That’s why it’s always a good idea for anyone facing charges to speak to an experienced criminal defense attorney, especially if there’s forensic evidence involved.

If you’d like an experienced Baton Rouge criminal defense attorney from The Ambeau Law Firm to evaluate your case, please send us an email or call (225) 230-1181.

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