A little trivia
The original play was written by Frederick Knott, who also wrote Dial M for Murder.
The original stars of the play were Lee Remick and Robert Duvall. I heard that Lee Remick left the production even before it opened but I couldn't find any info on that.
In the 1998 revival, you'll never guess who played Roat - Quentin Tarantino. Marissa Tomei played Susy.