Shirley MacLaine lost the lead role in The Exorcist (1973) due to her appearance in this movie, as director William Friedkin refused to cast her due to its similar theme of possession.
The first movie starring role for Perry King (Joel Delaney).
Two of the crew members were major figures in the development of Sesame Street: score composer Joe Raposo wrote most of the show's songs in its early years, and screenwriter Matt Robinson originally played Gordon and was one of the show's founding writers.
Perry King credited Shirley MacLaine for helping him with his performance in this movie. Being only his second movie role, MacLaine took the budding yet serious young actor under her wing during the production.
The actual New York City Public Library was used for the scene where Norah (Shirley MacLaine) looks up the news stories of Tonio Pérez's (José Fernández's) murder spree. Actual patrons served as extras during the sequence.