Brian Helgeland did writing on a film by Clint Eastwood.
Brian Helgeland . He is most known for writing the screenplays for L.A. Confidential ( for which he received the Academy Award for Best Adapted Screenplay ) , Mystic River , and A Nightmare on Elm Street 4 : The Dream Master . Mystic River is a 2003 American mystery drama film directed and scored by Clint Eastwood . The screenplay by Brian Helgeland was based on the novel of the same name by Dennis Lehane .