Black Mass, the adaptation of the true story of Whitey Bulger and the formation of the FBI's witness protection program, has picked up two new cast members.

According to The Hollywood Reporter, Adam Scott has been cast as FBI Agent Robert Fitzpatrick, while Benedict Cumberbatch will replace Guy Pearce as Billy Bulger, Whitey's brother. The duo joins Johnny Depp (Whitey Bulger) on the film, which has already begun shooting in Boston.

The original Black Mass: Whitey Bulger, the FBI, and a Devil's Deal, written by Dick Lehr, is a true account of the professional relationship between Irish mob godfather James "Whitey" Bulger and FBI agent John Connolly, and a deal between the two of them that had the potential to bring Bulger into the FBI, but ended up with Bulger manipulating Connolly to expand his criminal network.

Cumberbatch came to prominence for his role as Sherlock Holmes in the BBC's Sherlock, while Scott is best known for his role as Ben Wyatt in NBC's Parks and Recreation.

Directed by Scott Cooper, Black Mass is slated for release in October 2015.