I discovered this gem in Leonard Maltin's Turner Classic Movies guide. He'd only given it 2 1/2 stars, but I'm so glad I gave it the chance to prove itself. As others have already detailed, the cinematography, script and performances all make this relatively short film highly enjoyable, and suspenseful. Give it a try if you're looking for a serious topic dramatized in a slightly noir styling with a crime ring at the center of it.
(Here are a few more words to satisfy the IMDB requirement for a 600 character review. I'm keeping mine short and simple since others have already provided many fascinating facts, descriptions and details.)