In The Avenger, a killer is slicing the heads off of his or her victims, then sending them right to Scotland Yard, which seems pretty ballsy.
This pre-giallo was directed by Karl Anton, who made the 1957 German remake of Viktor and Viktoria and based on the 1926 Edgar Wallace novel of the same name.
The Executioner, the killer of this story, has been sending packages of those disembodied heads from different locations, along with letters taunting the police. When a Scotland Yard employee is one of the victims — who all seem unrelated — Detective Mike Brixan of Special Branch is called in.
There are just a few clues, like the black sedan seen at the scene of the crime and that two letters are offset in every letter The Executioner writes. Those letters match a script being written for a movie, which means that the murderer just might be one of the cast or crew.
Ingrid van Bergen, who plays the niece of one of the victims, has a giallo-like real life, as she shot her lover, money broker Klaus Knaths, dead and served five years of jail time, being released for good behavior, at which point she went back to acting.
You should also keep an eye out for a very young Klaus Kinski!
You can watch this on YouTube.