Tenderness of the Wolves
Die Zärtlichkeit der Wölfe (original)
A German serial killer preys on boys and young men during the so-called years of crisis between the wars. Based on the true story of Fritz Haarmann, aka the Butcher of Hanover and the Vampire of Hanover.
Starring Kurt Raab, Jeff Roden, Margit Carstensen, Ingrid Caven, Wolfgang Schenck, Brigitte Mira, Rainer Hauer, Barbara Bertram, Rainer Werner Fassbinder, Heinrich Giskes
Watch "Tenderness of the Wolves" on Amazon released in 1973. It's a crime and drama movie, and has a rating of 6.3 out of 10 from Imdb which is usually fine for this kind of movie, and is currently only available for purchase or rent.