I Saw What You Did is an American independent feature film of the psycho-thriller subgenre of horror. It was directed by William Castle with a screenplay written by William McGivern. It was produced by William Castle Productions and released theatrically in the United States on July 21st, 1965.
The "death in a shower" trope was made popular by Alfred Hitchcock in his 1960 thriller Psycho. Actress Janet Leigh played Lillian Crane, the unsuspecting murder victim of transvestite serial killer Norman Bates (played by Anthony Perkins).