A B mystery movie from the 40s and I don't know how easy it is to find, we got it on a 150 movie pack, but it's a good one. Originally based on the play Murder on the Second Floor by Frank Vosper, which apparently had already had some film versions of it made before this one but I doubt they're available anywhere.

A real B movie, I don't remember the names of anybody who was in it, but it was very interesting: set in a boarding house where everybody's got a secret and in the middle of it there's a murder and people wrestling down the stairs and a very funny part where the inspector tries to get answers out of a woman who refuses to speak on the grounds that she forgot her teeth!