The actor stars as an ex-convict in the Udayan Prasad-directed movie, which also features Kristen Stewart, Maria Bello and Eddie Redmayne.
Hurt told Parade: "I did spend a night in a maximum security prison in Angola, Louisiana, with a convict who was serving a life sentence.
"I also went back for ten days to talk to inmates. And I wanted to get rid of my New York actor body, so I went to a trainer who helped me beef up."
He added: "There's a difference between telling a story and living a story. I want you to feel that my character's living through a situation that you would believe.
"But you have to be careful. You can't really capture life without killing it. You can't open up a frog and see how his heart pumps without killing the frog. I don't want to kill the frog.
"I want to be part of expressing how wonderful and vital that privilege of life is. I ask myself on every page of a script and every word I say in a scene, 'Is this true or is this just a made up character?'"