How do you work with an expert witness? Very carefully. There’s two types of experts in the legal world: consulting experts and testifying experts. Consulting experts are those people who look at the facts and give you advice on how best to proceed in your legal case. Consulting experts can tell you where to look for evidence, what questions to ask, and how to prepare a case for hearing or trial. And since they work behind the scenes, they are effectively an agent of the attorney and thereby communication is protected under the attorney-client privilege.
Testifying experts, however, are completely different. There is no attorney-client privilege with a testifying expert. That means anything you tell the expert can be discovered by the opposing party even though you are the one who hired and pays for the expert. And since you want your expert to be viewed as neutral, you cannot tell the expert how you want him or her to testify. Instead, you want your testifying expert to come to an independent conclusion that (hopefully) favors you.
Obviously, you have to be careful of what you talk about with a testifying expert. The less you say, the better. But you need to say enough to get the facts and documents to the expert to review.
More importantly, you want to avoid having a consulting expert turn into a testifying expert because then everything you discussed with that person becomes fair game for the other side to discover at a deposition of the expert.
Select your experts carefully and then work with them carefully to be sure you don’t give away more information that you bargained for.