Stranger on the Third Floor (1940)

Reporter Michael Ward is the key witness in a murder trial. His evidence - that he saw the accused Briggs standing over the body of a man in a diner - is instrumental in having Briggs deemed guilty. But afterwards Ward's fiancée Jane is worried whether Ward was correct in what he saw and Ward becomes haunted by this question. Next Ward's neighbour is killed the same way as the man in the diner. But Ward is arrested for trying to point this out to the police. And so Jane goes out to try and clear Ward by finding the sinister stranger that Ward saw on the stairwell.