Kupon (1965)

Inspector Mejzlík once went to a garden restaurant and sat down at a table with a young couple of lovers. When the girl dropped her shop receipt on the floor, he began to tell her his story. One day the police found a dead girl in the fields outside Prague. She had been dead for two months, apparently murdered. It was not even possible to establish her identity. The perpetrator had robbed her, and all that was found in her purse was a tram ticket and a receipt from a shop for 55 crowns. And thanks to these two clues and the Commissioner's astute deduction and Detective Soucek's patient errands and questioning, the police not only found the girl's name, but also her killer.