The Lost One (1951, Germany) (aka Der Verlorene)

In actor/director-writer Peter Lorre's sole directorial effort after leaving the Hollywood studio system - an expressionistic, bleak, low-budget, film noirish crime-drama thriller reminiscent of Lorre's earlier film - Fritz Lang's M (1931, Germ.), and serving as a confessional symbol of Germany's collective war guilt:

• the protagonist: the chain-smoking and hard-drinking, world-weary resident physician Dr. Karl Neumeister (Peter Lorre) - working at a post-war displaced-persons refugee camp near Hamburg, delivering inoculations - and his flashbacked chronological story about the war years
• at the refugee camp, he met up with unrepentant Nowak (Karl John) - a renamed acquaintance and lab assistant from his past who was assigned to be his new helper in the camp; Neumeister was reminded of his guilty activities and overwhelmed when he recalled a traumatic war crime years earlier in 1943
• Note: Neumeister was known as Nazi Germany scientist Dr. Karl Rothe, while conducting secret research on pathogenic microbes in Nazi-era Hamburg, although someone was leaking results of his secret studies to the Allies
• Dr. Rothe's fiancee Inge Hermann (Renate Mannhardt) had been discovered to be working as a spy for the Allies; her duplicity was revealed by Hösch (aka Nowak) (Karl John), an undercover Gestapo Nazi hired by intelligence chief Col. Winkler (Helmut Rudolph) to determine the source of the leak of Rothe's research; Rothe was provoked by Hosch into a jealous rage to kill his fiancee Inge for the double-betrayal - for having cheated on him with Hosch, and for her treason
• the gripping scene of Rothe's murder (off-screen) of Inge (by strangulation) when she tried to win him back; as she knelt before him and closed her eyes, she helped him to gently caress and touch her hair, necklace, and neck before rising up (black covered the screen) and presumably tightening his hands around her neck; afterwards, he was seen sitting with her necklace no longer on her neck; he calmly put the necklace into his pocket; after the crime, the government authorities - including Hosch and Rothe - covered up the crime (making it appear like a suicide)

Rothe's Strangulation Murder of Fiancee Inge Hermann For Treason and Infidelity

• Rothe's transformation into a pathological, cold-blooded serial killer - and the powerful scene of his murderous intent in an empty staircase with an intuitive, street-walking prostitute (Gisela Trowe) (who looked at him, recognized him as a death-threatening man filled with evil, labeled him a "Killer!", and ran off)
• Rothe's subsequent murder of a seductive married woman (Lotte Rausch) in a train compartment, as he stared at her while lighting his cigarette, and she realized - although too late - that she was about to be murdered due to the sick impulses of Rothe
• the concluding downbeat pair of chilling sequences: Neumeister's revenge against Nowak by point-blank shooting him with a gun, and then his own self-destructive suicide when Neumeister walked out to nearby train tracks, and stood with his back to an oncoming train, covered his face with his hand, and awaited obliterating death

Shooting Nowak	Neumeister's Suicide