The Laughing Policeman is an American police procedural film loosely based on the 1968 novel The Laughing Policeman by Maj Sjöwall and Per Wahlöö. The setting of the story is transplanted from Stockholm to San Francisco. It was directed by Stuart Rosenberg and features Walter Matthau as Detective Jake Martin.
A busload of passengers, including off-duty police detective Dave Evans, are gunned down and killed. Evans, on his own time, has been following a man named Gus Niles in search of information linking businessman Henry Camarero to the murder of his wife, Teresa, two years earlier.
Evans was the partner of Detective Sergeant Jake Martin, a veteran but cynical member of the Homicide Detail working the bus massacre investigation. Jake originally investigated the Teresa Camarero case and has been obsessed with his failure to “make” Camarero for the murder. Jake returns to it after many dead-end leads (including a disastrous confrontation with a deranged amputee who takes hostages at gunpoint) in the bus investigation. Niles was killed on the bus as well, and it was Niles who provided the alibi that enabled Camarero to cover up his wife’s murder.