(Some Spoilers) Parking his car just before the #14 bus reached the bus stop the killer calmly walks in takes a seat and assembles his semi-automatic "grease gun". Then without saying a word opens fire on the passengers and bus driver killing all but one of them, an elderly survivor later died at the hospital, on the spot as the bus crashed into a small Chinatown park. On the scene of the massacre is SFPD Let. Jake Martin, Walter Matthau, who after inspecting the victims of the "Death Bus" is shocked to find that one of them is Det. Dave Evens, Anthony Costello, is his partner! What was Evens doing on that bus?

Going to see his live-in girlfriend Kay Butler, Cathy Lee Crosby, Let. Martin finds that Evens who was out sick for the entire week. Telling her that he was on the Teresa Camerero case a case that was adjudicated almost two years ago? Teresa was murdered and her husband Henry, Albert Paulsen, who was tried for her murder but was found innocent in a court of law. What's even more ironic is that the star witness who got Henry off with the alibi that he was with him at the time of Teresa's murder was Gus Niles, Louis Guss! Who just happened to be one of those who were killed like Evens on bus #14!

Let. Martin and his new partner SFPD inspector Leo Larsen, Bruce Dern, are put on the "Death Bus" case and they painstakingly tie the Teresa Camerero murder to it. Not only that but that Det. Evens had a very personal relationship with Teresa and was on his own, without the go ahead from his police superiors, out to solve her murder and it was that very reason that lead to his death.

Slow moving but effective police/crime/drama with Let. Martin and Inspector Larsen as the oddest of odd partners with Martin not saying a word unless he absolutely has to. and Larsen never keeping his mouth shut for even a second. Going through the sleazy sex parlors and seedy bars nightclubs of San Francisco the two track down the killer but are unable to arrest him until he breaks the law again.

It turned that the killer was acting in concert with Niles to get Evens on the bus in order to murder him. We even see Niles acknowledged the killer as he entered the bus. What did happen was that Niles was double-crossed by the killer as he opened fire on everyone on board including him. Thus having Niles not around to finger him in case he later wanted to make a deal with the police in order to save his neck from ending up in the San Quinten gas chamber.

The ending of "The Laughing Policeman" is a bit overdone with a totally unnecessary car chase sequence as well as a repeat of the bus massacre that began the film. But this time around it was the killer, not the innocent passengers and bus driver, who got massacred.