THE KILLER IS LOOSE (1956) NOIR ALLEY.
When police go to arrest a suspect involved in a bank robbery, after they knock, and demand his surrender, the suspect fires through the closed door. Upon bursting into an apartment occupied by the criminal, Det. Sam Wagner (
Joseph Cotten) shoots a shadowy figure which turns out to be the criminal's wife. She is killed, and the criminal Leon Poole (
Wendell Corey), surrenders, but vows revenge for his wife's death.
Several years later, he is and has been a model prisoner, and is in a trustee situation where he can escape. Now he has killed the guard, and is leaving a trail of death behind him. All but one of the authorities assume that he is out to kill Detective Wagner; this one man realizes Poole's target is not Wagner, but Wagner's wife. That wife (
Rhonda Fleming), had been begging her husband to leave police work and do something safe for a living. Now she is that much more insistent, & Wagner must protect her without letting her know
she is in danger.
As usual, Muller details the story behind the story.