William Lee was a con-man in Mr. Monk Is Up All Night. Working with waitress Zena Davis and a fake drug dealer, he pretended to be a part of a drug deal with the dealer and Jacob Posner. Lee then claimed to be an undercover police officer, at which point the drug dealer "shot" him and escorted Posner away. While the drug dealer got hush money from Posner, Lee and Davis cleaned up the "crime scene" to make it seem like none occurred. Unfortunately for him, the initial "drug deal" was witnessed by Adrian Monk, who called the police, although not before the scene was cleaned and Lee snuck out. Lee was later encountered by Monk at a train station, where he claimed to not know anything about the "murder" when questioned by police. While later talking to Posner, Monk, Leland Stottlemeyer, and Randy Disher mentioned that Lee was alive, causing Posner to recognize he'd been scammed. Angry, he went to the train station and killed Lee for real. Posner was later arrested for Lee's murder, as well as the attempted murder of Davis and the drug dealer.