Behind Green Lights (1946) on Netflix

Plot summary

Janet Bradley visits the apartment of Walter Bard, a private detective who works in blackmail. Bard holds letters that would damage someone close to her, and when she cannot raise the money he demands, she takes the letters by force and leaves his gun in his car. At the police station, Lt. Sam Carson and the reporters on the night beat see Bard's car roll up with his body inside. Carson spots Janet's name in Bard's appointment book and has her brought in for questioning. Her father, Luther Bradley, is the reform candidate for mayor. Max Calvert, a newspaper publisher backing Bradley's rival, pressures Carson to arrest Janet so the scandal will hurt her father's campaign. Carson wants to investigate before he charges her, and Janet will not say why Bard was blackmailing her.