This was initially intended to lead to a spin-off TV series, but Universal decided to go with Night Gallery (1969) instead.
Larry Richmond took Aline Wiley's body away from the shore in an earlier draft of the script, and the police interrogation scene with Richmond was longer in this original script.
A scene at an occult book store was included in the original script, but was ultimately excised from the film.
Another scene in the original script that didn't make it into the movie, had David trying to get Leila to go inside an old Spanish church with him. In the course of the scene Leila became increasingly more agitated and annoyed, further arousing David's uneasiness about her.