Only the Dead Can Answer (1969)

Police captain Wójcik conducts an investigation into the murder of a cashier from a state-owned enterprise. Despite seemingly numerous leads, the investigation gets stuck in a dead end – the victim had no enemies and nothing was stolen. Despite closing the case Wójcik feels that the key to solving the mystery is the murdered cashier and his past. Exploring this plot, he discovers a full-fledged spy affair, however, trying to catch the real murderer, he’ll have to risk his life, health and career.