"Stranger on the Third Floor" is a suspenseful film noir because it deals with is a man really the killer and how do you know? A reporter must deal with that, he is the only witness to a murder but in his mind he starts to second guess him, then when another murder happens and he's the prime suspect the real story starts to pan out.
The actors were good, Margaret Tallichet and John McGuire had good chemistry. The little bit that we get to see Peter Lorre makes us want to see more and that's what hinders the movie but what screen time he has, he dominates. It ends way too quickly and his character doesn't get a chance to actually developed which makes the movie not that impressive. There are scenes, the dream sequence where McGuire's character thinks that he's going to prison and before that Elisha Cook Jr. on trial yelling he's not guilty, that give the movie that paranoia feel which is a nice touch.
Overall the movie isn't too bad, it does have potential but it loses out when they give little screen time to the some of the characters and to even the actual killer! The ending could have gone differently. It does have it's decent moments and the plot works just the characters could have been developed a lot more. So for an overall rating of this movie it's between 2.5 to 3 stars out of 5. It's decent but not a wow movie, it started out wow then ended with a dud!