Many historians and critics claim this little gem, STRANGER ON THE THIRD FLOOR, is the very first true film noir.
But I'm getting ahead of myself here a little bit.
The plot is a classic set-up: reporter Micheal Ward gets the scoop of a lifetime when he happens upon a murder and becomes the key witness at the trial of the petty criminal, Joe Briggs, found at the scene standing over the body. Briggs claims he's innocent and claims that he found the victim already dying. Ward's testimony convicts Briggs, who is sentenced to the death
This turns out to be wonderful for Ward's career, but he soon has doubts (planted by his fiancee) as to whether Briggs really is the killer or just an unlucky bypasser as he claimed. When a similar murder occurs and Ward is again on the scene, he reports the crime - only to be accused by the police of being the killer himself.
The story is interesting and contains one of the most surreal, disturbing dream-sequences mid-century Hollywood ever devised. And, as I said, the film looks incredible and makes astounding use of light and shadow to create what would become the archetypal film noir look.
You can't help but be suspicious of a young Peter Lorre when he's lit that way. (I mean, he is the titular stranger, but still...)