'American Sniper' Stars, Writer Went Beyond Chris Kyle's Book

'American Sniper' New York Premiere - H 2014
Charles Sykes/Invision/AP

Plus Bradley Cooper's co-stars reveal how they reacted to the actor's much-discussed transformation

Bradley Cooper's new film American Sniper, directed by Clint Eastwood, is both based on the autobiography of the same name by accomplished marksman Chris Kyle (and co-authors Scott McEwen and Jim DeFelice) and parts of Kyle's life not included in the book.

Screenwriter Jason Hall began scripting the film while Kyle, who was killed at a shooting range in February 2013, was still alive, and before Kyle wrote the book. Hall said he tried to incorporate "the other side" of the book's late subject into the movie — specifically who Kyle was outside of war.

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"The book didn't portray … the softer side of who [Kyle] was before the war and some of the healing that he encountered after the war and how he found a way to help all these vets," Hall told The Hollywood Reporter at American Sniper's New York premiere Monday night. "And I thought that was the powerful story."

After Kyle was killed, Hall said he felt a strong responsibility to portray the skilled sniper accurately.

"There was a lot of pressure to get it right because his wife wanted us to get it right. And we wanted to get it right for those kids. He's got two kids left behind, and they're 4 and 6, so you remember very little from that age. Hopefully we got this right so that they can have this to remember him by," Hall added.

Cooper's co-stars in the film also went beyond the book to prepare themselves to play Kyle's fellow service members.

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Luke Grimes, who plays Navy SEAL Marc Lee, said that he spoke to Lee's girlfriend at the time, who sent him photos and emails they exchanged, "just to give me a better understanding of who he was as a person," the actor said.

Cory Hardrict, who plays another SEAL, also tried to get into the military mindset by watching war movies, like Black Hawk Down.

Nashville actor Eric Close, meanwhile, who has a small but significant part in the film, said that since his section of the story wasn't in Kyle's book, he relied on the script and spoke to the writer during his week in Morocco, flying out and filming his scenes around completing an episode of the ABC drama.

Ultimately, though, Close said he just trusted Eastwood.

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"He's the man. You've just got to trust his instincts," the actor said, describing the experience of working with Eastwood as "a dream come true."

"I never knew if it would ever happen," Close said. "I've known him for a number of years, and then this one came about, and the next thing I knew I was on a plane to Morocco."

Close and Cooper's other co-stars also marveled at the two-time Oscar nominee's much discussed transformation into Kyle, including putting on 40 pounds of muscle and adopting the Navy SEAL's Texas drawl.

"He embodied that character and I thought he really paid a great respect to Chris' memory and legacy," Close said. "He really did it honor, I thought. It was an amazing performance, and very subtle."

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Hardrict added: "He surprised everybody. You see him now, and it's like night and day. … He looked like a different guy. He had a beard and was chewing the tobacco. He had the accent down. It was awesome."

Grimes said, "I hadn't heard that he had put on all this weight, so the first day he shows up and I didn't even recognize him. He was so committed the whole time."

Sienna Miller is also fairly unrecognizable in her role as Kyle's wife, Taya, who was also on hand for Monday's Jazz at Lincoln Center screening in Manhattan.

"It's not a conscious thing," Miller said of her transformation. "Obviously I had brown hair, so that's different. You try to capture the idiosyncrasies that make someone. The facial movements, the physicality that's obviously very different to my own. And you try to inhabit something. So if it's unrecognizable then I've done my job."

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Cooper, meanwhile, took on an additional job in this film, that of producer.

When asked what he learned about that part of filmmaking from his experience on Sniper, Cooper said, "a tremendous amount."

"Everything that goes into making a movie from buying the rights to a book to standing right here talking to you," he added on the red carpet, saying he really learned about how collaborative the process of making a movie is. "You want to surround yourself with people who have the same kind of work ethic that you do."

Warner Bros. execs Sue Kroll, Greg Silverman, Dan Fellman and Kevin Tsujihara were also on hand for the film's New York premiere along with Cooper's Elephant Man co-star Alessandro Nivola, Inside the Actors Studio host James Lipton, Benjamin McKenzie, Tia Mowry, Montel Williams, Bob Woodruff, actress and Fox News contributor Stacey Dash, Stephen Baldwin and others.

American Sniper opens in select theaters on Christmas Day, expanding nationwide on Jan. 16.