Behind Green Lights (1946)

An unscrupulous private investigator with a penchant for blackmail is found dead in a car and the leading suspect is Janet Bradley, the daughter of a mayoral candidate. With the election just weeks away, shady and ruthless individuals muscle the medical officer into switching the corpse with another body. Lieutenant Sam Carson, one of the few good apples in the bunch must find a way to get to the bottom of it all.