Claim: Brian Helgeland did writing on a film by Clint Eastwood.

Brian Thomas Helgeland -LRB- born January 17 , 1961 -RRB- is an American screenwriter , film producer and director . He is most known for writing the screenplays for L.A. Confidential -LRB- for which he received the Academy Award for Best Adapted Screenplay -RRB- , Mystic River , and A Nightmare on Elm Street 4 : The Dream Master . Helgeland also wrote and directed 42 -LRB- 2013 -RRB- , a biopic of Jackie Robinson , and Legend -LRB- 2015 -RRB- , about the rise and fall of the Kray twins .