In the words of Black Mass’ director, actress Sienna Miller delivered an extraordinary performance for his movie. But not even that spared her from being taken out of the final cut, according to him, for narrative reasons. He felt that Miller’s character didn’t really add much to the plot. This remains a very peculiar move, mainly because she played the part of Johnny Depp’s partner, who was actually the main character... The movie is based on a book, which in turn is based on real-life events. And in real life, Miller’s character helped the protagonist to get away and kept him from being captured for about 16 years.