Rent The Murderers Are Among Us (1946)

Susanne Wallner (Hildegard Knef) returns to the ruins of Berlin from a Concentration Camp after WW2 to discover that someone else lives in her apartment: Dr. Hans Mertens (Wilhelm Borchert), the war made him depressive and he drinks a lot of alcohol. Susanne asks him to go but he doesn't want to, so they share Susanne's apartment and even discover their sympathy and then their love for each other. That encourages him a little, of course. But then he hears that Ferdinand Brückner (Arno Paulsen) is still alive and also lives in Berlin. Brückner was his Captain during WW2, he gave the order to kill more than 100 innocent people, many children and women among them, on Christmas 1942 in Poland.