The Secret Killer
Le vampire de Düsseldorf (original)
A true story of Peter Kurten, a serial killer who committed nine murders and many other offenses in Dusseldorf during the Great Depression era.
Starring Robert Hossein, Marie-France Pisier, Roger Dutoit, Annie Anderson, Anne Carrère, Michel Dacquin, Norma Dugo, Paul Pavel, Robert le Béal, Colette Régis
Watch "The Secret Killer" on FlixOlè released in 1965. It's a crime and action & adventure movie, and has a rating of 6.7 out of 10 from Imdb which is usually fine for this kind of movie.