An Occasional Hell (1996)

When a married man is found murdered, and his girlfriend is missing, the police suspect the wife of the murdered man. The wife turns to a professor at college who is a medically disabled ex-cop to help clear her. Not wanting the job at first, he eventually does begin to investigate the crime while fighting the demons and the pain of his own life. The clues are scarce, but one clue is that the man was murdered with an unusual weapon - a musket.