I Saw What You Did is a 1965 American horror film released by Universal Pictures and starring Joan Crawford and John Ireland. The plot follows two teenage girls who find themselves in serious danger after making a prank phone call to a man who has just murdered his wife. The screenplay by William P. McGivern was based upon the 1964 novel Out of the Dark by Ursula Curtiss. The film was produced and directed by William Castle. Wikipedia
Libby: I saw what you did, and I know who you are.