As not to cause an alarm the SS are secretly investigating the murders. When they arrest an innocent man for one of the killings, a lone police detective goes to great lengths to prove his innocence, but unfortunately for him the SS isn't interested in justice only keeping the population under their boot.
The guy who plays the investigator does a fine job, but it's the serial killer (played brilliantly by Mario Adorf) that steals the show. One look at him and you know he's bad news. You wouldn't want to be stuck in a broken elevator with this guy! But even more disturbing are the SS guys who lurk around behind the scenes pulling the strings with no concern for right or wrong or even who dies in the process.
If you can find a copy it well worth watching. I'm deeply ashamed it took me 524 reviews to finally get to Siodmak, but I will try to make up for it soon...then again I think I promised the same thing about Allen, Bergman, Ford, Lang, Ozu, Kurosawa, Vidor, Bunuel and Mizoguchi and look at how fucking far behind I am! Hell, I don't think I've even review one single David Lynch movie yet!!!
This has to be one of the earliest examples of "fuck" used in a film. Remember though Kurosawa was using "asshole" all the way back in 1949!