Director Danny Steinmann was upset with the final cut of the film because it missed most of the major scares. He had his name removed from the movie and was credited under the pseudonym "Peter Foleg".
Director Danny Steinmann was apparently very difficult to work for on the set and some of the actors barely spoke to him at all. It's said that he had absolutely no idea how to talk to people, especially actors.
The project originally began as a screenplay by Kim Henkel and Michael Viner. The final screenplay was so radically altered that both men were not credited. Henkel and Viner's screenplay was eventually adapted into the book "Deadly Encounter" by Richard Woodley in 1980.
The last name Keller is phonetically the Danish word for basement, "Kælder" which the film was releases as in Denmark, Kælderen.