The Locked Room
Maj Sjöwall & Per Wahlöö

Detective Martin Beck returns in the 7th book in this mystery series set in Stockholm written by husband and wife team, Sjöwall and Wahlöö. Beck is back to work after a medical leave and is assigned to a case involving the discovery of the decomposing body of an elderly man who was found in a room that appears to have been locked from the inside with no weapon in evidence. To complicate matters further, Beck begins to suspect that a second crime, a bank robbery across town where a security guard was shot, is related to the first case.