The Laughing Policeman (1973)

When a gunman opens fire on a crowded city bus in San Francisco, Detective Dave Evans is killed, along with the man he'd been following in relation to a murder. Evans' partner, Sgt. Jake Martin, becomes obsessed with solving the case.

Directed by: Stuart Rosenberg

Starring: Walter Matthau, Bruce Dern, Louis Gossett Jr., Albert Paulsen, Anthony Zerbe, Val Avery

Links: IMDb, Movie posters, Movie stills