I Saw What You Did (1965) is a Universal Pictures feature film starring Joan Crawford and John Ireland in a tale of murder. The screenplay by William P. McGivern was based upon the 1964 novel Out of the Dark by Ursula Curtiss. The film was directed and produced by William Castle, and co-produced by Dona Holloway. The 2002 widescreen DVD release used the film's original 1965 poster title "I Saw What You Did" And I Know Who You Are!.
When two mischievous teens, Kit (Sara Lane) and Libby (Andi Garrett) are home alone with Libby's younger sister, Tess (Sharyl Locke), they begin randomly dialing telephone numbers and telling whoever answers: "I saw what you did, and I know who you are." One call is placed to Steve Marak (Ireland), a man who has recently murdered his wife (Joyce Meadows) and disposed of her body in the woods. Believing his crime is known, he decides to track down the girls and silence them. Neighbor Amy Nelson (Joan Crawford) is in love with Marak and has been trying to woo him away from his wife. She inadvertently saves Libby from being killed and is stabbed to death by Marak. He then closes in on the girls but their parents and the police arrive in time to stop him
(This is information generated from a Wikipedia article, licensed under the GNU Free Documentation License.)