Most courts hold that testifying experts must produce all materials that they review (or create) in connection with their testimony. Does the same rule apply to experts who began as non-testifying consulting experts, but later choose to take the stand?
As in other areas, courts go both ways. Some courts allow such experts to withhold documents they have prepared in their role as consultants. See, e.g., Messier v. Southbury Training Sch., No. 3:94 CV1706 (EBB), 1998 U.S. Dist. LEXIS 23221, at * 7 (D. Conn. June 29, 1998). However, the recent decision in Western Resources, Inc. v. Union Pacific Railroad Co., No. 00-2043-CM, 2002 U.S. Dist. LEXIS 1911 (D. Kan. Jan. 31, 2002), took the opposite approach and required a testifying expert designated in 1999 to produce work he had prepared over the previous nine years as a consulting expert.
Parties deciding whether to have someone who has been acting as a consulting expert take the stand as a testifying expert must check ahead of time to see if such a tactic will require them to produce all of the materials that the expert prepared while a behind-the-scene consultant.