The Laughing Policeman
When a gunman opens fire on a crowded city bus in San Francisco, Detective Dave Evans (Anthony Costello) is killed, along with the man he'd been following in relation to a murder. Evans' partner, Sgt. Jake Martin (Walter Matthau), becomes obsessed with solving the case -- but all the witnesses are dead. Martin enlists a new partner, Leo Larsen (Bruce Dern), to help with the frustrating case, and when the pair is told to drop the investigation, they disobey the orders and close in on the killer.