I have a third shot left. I'll spend it with
The Laughing Policeman (1968), by
Sjöwall and Wahlöö. It earned a 'Best Novel' Edgar Award from the Mystery Writers of America. The American police procedural film, The Laughing Policeman (1973) featuring Walter Matthau, is a loose adaptation of the novel.
A gunman shoots the passengers of a public transport bus with a sub-machine gun; he kills eight people (including Detective Ake Stenström), and wounds one. Detective Beck and his team suspect the mass-murder is to disguise the murder of Detective Stenstrom, who was spending his free time investigating the sixteen-year-old murder of a Portuguese prostitute.