Beyond Betrayal (1994)

Joanne is married to Bradley, who's a cop and who abuses her. One day she decides to run away. She then meets Sam, who is separated from his wife, who is obsessed with him. Bradley finds Joanne and the lead takes him to Sam's boat. Now his wife is on the boat and somehow she's killed. The police suspect Sam because she was stalking him and because of certain peculiarities in his actions on the day she died. Joanne knows that it's Bradley who did it but is too afraid to come forward and Bradley has another cop alibi him.