Shock (1946)

"He never dreamed what it would all lead to...and she didn't care !"

In this thriller, psychiatrist Dr. Cross kills his wife and expects to get away with murder, until he discovers that the slaying was observed by a next-door neighbor, Janet Stewart. As Janet attempts to convince her husband of the doctor's dastardly deed, Cross shows up to advise him that Janet is in dire need of some in-depth counseling.