Pretty Poison (1968)

She's such a sweet girl. He's such a nice boy. They'll scare the hell out of you.
Crime / Drama / Romance / Thriller • 89 minutes  7.2/10
Starring: Anthony Perkins Tuesday Weld Beverly Garland John Randolph Dick O'Neill Clarice Blackburn Joseph Bova Ken Kercheval and others.
Director: Noel Black Screenplay: Lorenzo Semple Jr. Director of Photography: David L. Quaid Producer: Marshall Backlar Noel Black Editor: William H. Ziegler Original Music Composer: Johnny Mandel
Released • July 18, 1968

When a mentally disturbed young man tells a pretty girl that he's a secret agent, she believes him, and murder and mayhem ensue.

A.K.A. DE: Der Engel mit der Mörderhand  ES: Un maravilloso veneno