You retain an expert for the defense.

Opposing counsel retains the same expert for the plaintiff.

What then?

This situation occurs more frequently than you’d expect, and it can prompt heated battles.

One example — although a fairly easy case — was In re Diet Drugs Prods. Liab. Litig., MDL No. 1203, 2009 U.S. Dist. LEXIS 54580 (E.D. Pa. June 26, 2009). There, Wyeth contacted Steven Kawut, M.D., in October 2006 about the possibility of Dr. Kawut consulting for the defense in the Diet Drug Litigation. According to their later declarations, two lawyers for Wyeth sent Dr. Kawut material in a diet drug case and discussed Dr. Kawut’s opinions “on three or four occasions.” Id. at *3. The lawyers also told Dr. Kawut Wyeth’s “‘theories of the case, general and case specific defenses in diet drug litigation,'” case “‘themes,'” and “‘potential strategies for addressing the opinions of other experts.'” Id.

Another lawyer (from a different firm) representing Wyeth submitted a declaration to similar effect. Id. at *3-4.

And Dr. Kawut had signed a letter agreement with Wyeth to serve as a consultant in a second diet drug case. The letter agreement provided: “Whether or not the agreement is terminated, you may not work for or represent any other person or entity in connection with legal proceedings involving fenfluramine or dexfenfluramine.” Id. at *5.

Then Dr. Kawut was designated as an expert for a plaintiff in yet a third diet drug case.

In response to Wyeth’s motion to disqualify Dr. Kawut from testifying in the third case, Dr. Kawut submitted an unverified letter, addressed “to whom it may concern,” saying that he didn’t notice the language in his retention letter “indicating the expectation that my consulting would be exclusively for Wyeth.” Id. at *6.

Fish — obtain barrel!

The legal standard permits experts to be disqualified if they’ve previously worked for the adversary and obtained confidential information during that employment. In Diet Drugs, the record on that point was awfully strong for Wyeth, and plaintiffs didn’t exactly put up a fight by filing only an unsworn letter in response.

Judge Bartle granted Wyeth’s motion to preclude Dr. Kawut from testifying for the plaintiff or consulting further with plaintiff’s attorneys. Id. at *9.

There are three lessons to be drawn from this case:

First, when moving to disqualify an opposing expert, it’s good to have lots of proof on your side. Here, Wyeth submitted the declarations of three different lawyers describing their conversations with the expert, and Wyeth also submitted a signed letter agreement forbidding Kawut from consulting for others.

That’s a whole lot better record than folks will have in many of these situations. If one of these motions turns into a swearing contest — one defense lawyer says he revealed confidences to the expert, and the one expert denies it — the turf gets awfully mushy. The defendant can’t disclose what secrets it revealed to the expert (because, after all, they’re secrets) and the judge won’t know who to believe. It’s good to have multiple witnesses and a signed document on your side.

Second, if you’re ever opposing a motion to disqualify an expert on this ground, take it seriously. It’s surely worth the effort to obtain a penalty-of-perjury declaration from the expert, rather than just an implausible, and unsworn, letter addressed “to whom it may concern.”

Finally, this case didn’t raise the truly contentious issue: Whether disqualification of an adverse expert taints the opposing counsel who retained (and worked with) that expert, requiring disqualification not just of the expert, but of opposing counsel as well. If you ever file one of those motions, expect a real battle: Opposing counsel can usually find a substitute expert, but opposing counsel doesn’t like to be knocked out of a representation and lose a fee.

There’s a pretty large body of law addressing when counsel who worked with a disqualified expert must themselves be disqualified. If you’re ever in this situation, study that law, examine the evidentiary basis for your motion to disqualify both the expert and opposing counsel, and, if you choose to file the broader motion, gird your loins for a battle royale.