El Policia que riu (1968)

On a cold and rainy Stockholm night, nine bus riders are gunned down by an unknown assassin. The press, anxious for an explanation for the seemingly random crime, quickly dubs him a madman. But Superintendent Martin Beck of the Stockholm Homicide Squad suspects otherwise. This apparently motiveless killer has managed to target one of Beck's best detectives-and he, surely, would not have been riding that lethal bus without a reason.