Throw Momma From the Train (1987)

Larry Donner is a author and writing professor who tutors people who want to write books. Larry's life has become a misery when his Ex-wife has published a book he wrote under her name and has gotten rich over it. Owen Lift, one of Larry's students offers Larry to kill Larry's Ex-wife and in return Owen wants Larry to kill his horrible mother. Larry thinks it is a joke, until he learns Owen killed his Ex-wife and he has become the prime suspect.