Star Jason Robards thought he was miscast in this project.

The name for the type of horror genre of plays that were staged at the "Rue Morgue Theatre" in Paris, France was "Grand Guignol". The name of the early 20th century theatre troupe that staged the plays there was "Cesar Charron's Company".

In an interview included on the movie's the DVD, director Gordon Hessler said that he thought the majority of people knew the ending of the source short story (the film is a remake and had been shot more than once before), so Hessler thought he would re-imagine the story, and as such introduced new story elements.

Another version of the film's source Edgar Allan Poe short story, but made for television, Le double assassinat de la rue Morgue (1973), was released within a couple of years, and the previous version, also made for television, had been first broadcast only about three years earlier [See: Detective: The Murders in the Rue Morgue (1968)].

Debut theatrical feature film of actress Brooke Adams who appeared uncredited as a nurse.

The movie's closing credits declare that this motion picture was: "Filmed entirely on location in Spain".

The film was made and released about exactly one hundred and thirty years after its source short story of the same name by Edgar Allan Poe had been first published in 1841.

The movie has been released on its own on DVD as well as on a double feature in 2003 with Cry of the Banshee (1970) which was also directed by director Gordon Hessler.

Nearly all of Lilli Palmer's role was removed in post-production.

Second and final of two filmed Edgar Allan Poe adaptations directed by Gordon Hessler. The first had been The Oblong Box (1969) made about a couple of years earlier.

The movie introduces story elements akin to Gaston Leroux's "Phantom of the Opera". Actor Herbert Lom had portrayed Professor L. Petrie aka The Phantom in Terence Fisher's 1962 version [See:The Phantom of the Opera (1962)].

Italian censorship visa # 60707 delivered on 19 July 1972.

Robards' character is aptly named Charron, a variant spelling of Charon, the mythological ferryman who transported the souls of the newly dead across the river Styx from the Earth to Hades.