You can read the original script by Taylor Sheridan for free on platforms like IMSDb (Internet Movie Screenplay Database) Indieground Films Trailers and Behind-the-Scenes:
If you haven't seen it yet, Sicario follows an idealistic FBI agent (Blunt) who is enlisted by a government task force to aid in the escalating war against drugs at the border area between the U.S. and Mexico. index of sicario 2015 free