Deadly Matrimony(1992)

Alan Masters is a despicable businessman with his hands in organized crime. He marries Diane, a kind and gentle woman, and abuses and batters her viciously. Sergeant John Reed has had enough of his city's organized crime and, against the wishes of his dirty-cop superiors, tries to get evidence against Alan Masters. After Alan finds out that Diane has been helping Reed, he beats her to death...and its up to John Reed to put him away for it, and clean up the dirty cops that want to stop him. Part I starts with Diane's death and then, in a flashback, details her struggles against abuse and Reed's struggles as he coaches her to gather evidence against Alan. Part II deals with Reed's struggles with intimidating cops.