Law & Order · S1, E22
The Blue Wall
Asst. D.A. Stone is angered when incriminating evidence on a computer disc is erased, destroying his case against George Bakewell, Arthur Vickery, and Jim Grierson of the Manhattan Mercantile Bank. He is convinced that someone in the New York City Police Department altered the evidence, and an Internal Affairs investigation is put into action. Detectives Greevey and Logan agree to investigate behind the scenes to help Captain Cragen, who has become IAD's prime target.
