Joe Frady, "The Parallax View"
Harry Caul is a surveillance expert – one of the best in the field. But he's got this weird hang-up about his surveillance data being used to facilitate murder. So when a seemingly innocent conversation he's hired to record begins to tweak his suspicions, he goes to lengths to protect the people involved. But just because you know too much doesn't mean you understand anything – and that's a lesson that Harry Caul learns the moderate-to-severe way.
Nora Davis, "The Girl Who Knew Too Much"
Often considered the first "giallo" thriller in movie history, "The Girl Who Knew Too Much" utilizes the common plot giallo plot point of a character who learns too much about a serial killer on the loose – and who thus becomes a target of the murderer. In Davis' case, she is dismissed by many as a "hysterical female," so she ends up having to entrap the killer herself.
Marcus Daly, "Deep Red"