A brutal murderer was widely known in the 1920's in Germany, nicknamed The Vampire of Düsseldorf (hence the title). He got captured and he appeared to be Peter Kürten. In this version of events we follow Peter committing his crimes. A laborer who pretends he's from high society. There's much attention for the unstable political situation in the days of the Weimar republic. There are fascist everywhere, burning books, beating people up, etcetera.
Watching a serial killer doing his thing is a actually quite weird type of film to watch. But it exists for decades and keeps on fascinating people, until this day (for example Henry, Portrait of a serial killer, or series like The Fall and Dexter). Le vampire de Düsseldorf is an early example from 1965. But a film about (supposedly, director Fritz Lang denied it) the same killer, M., is even older, even from the same year as when Kürten was executed (1931).
The subject isn't very original. As many others already have mentioned, M. by Fritz Lang is a much better film. It's not so much about the killings, rather about psychology, fear and sentiments. As others also have mentioned, there's not much German about this film, not even an attempt to. This film lacks in original storytelling and in realism.
However, the good thing is: I found this film surprisingly stylish. Robert Hossein (who wrote and directed the film, and played the lead) was by then already an experienced film noir director, who knew how to capture the attention with silence, as he did in La Mort d'un Tueur. The street scenes at night are quite marvelous. The camera movements are lovely to see. Many pretty shots, as for example the distant shot of the bar Eldorado, the shot with Anna and all her mirrors, or the following through the streets. Those are absolutely worthy of the predicate film noir. I rate this 7/10, mostly for style.
Unrelated to the review, but I also like the idea of a bar with phones in which, for example, table 14 could call table 8. Apparently a common thing in the 20's. A funny concept that a smart person perhaps can revive again.