Jason Hall's screenplay for "American Sniper" earned him an Oscar nomination Thursday. It's not simply a look at the experiences of Chris Kyle, the Navy SEAL considered the most lethal sniper in U.S. military history, he said in a recent phone call. It's an attempt to describe war "in a way that it hadn't been portrayed before."

Hall began the project in 2010 before the marksman's memoir "American Sniper" was published, basing his early script on Kyle's early drafts of the book and many interviews.

"I heard of some of his accomplishments over there. I heard of the 2,100-yard shot" in which he killed an insurgent aiming a rocket at a U.S. convoy.

Hall traveled to Texas after Kyle's four tours in Iraq to meet him and understand who he was, why he did what he did and how it affected him.

Early on he felt that Kyle carried "a sense of turmoil. I looked in his eyes and shook his hand and it seemed to cost him dearly. He didn't feel like he was home to me." Meeting Kyle's wife made Hall feel "she also did four tours staying home and raising these kids. I felt that in that relationship was a story that I hadn't seen before. How had they survived that 10 years and stayed married" when the divorce rate among Navy SEALs is over 90 percent.

Then in 2013 Kyle was killed by a troubled former Marine he was trying to help at a gun range. "I turned in the script and the next day he was murdered," Hall said.

For him, Kyle's life story was not ending but beginning again. He dug deeper, interviewing Kyle's widow for hundreds of hours, understanding him in a way he had not grasped before. His new script revealed who Kyle was before the war, his emotional sacrifice in battle and what he lost.

"The difficulty he had transitioning back and forth from civilian life to [the war zone] was profound, something I hadn't seen in other films. I realized early on that whatever problems we had with this war, whatever decision we made about it, [the soldiers] had made a much harder decision. Their decisions affected the rest of their lives. It was a moral dilemma that would forever alter Chris' life."

Hall estimates that less than half the film is based directly on Kyle's book. One chapter that was not brought to screen concerned former Minnesota Gov. Jesse Ventura, who sued Kyle's estate for defamation after Kyle's book said he beat a man (later identified as Ventura) for insulting SEALs. In a court settlement Ventura was awarded $1.8 million.

"In the book you come away with the sense that [Kyle was] this jaded character who's a true patriot but also had a real chip on his shoulder. The reality of Chris was something different. All these guys go out, have one too many, end up getting in a bar fight and high-tail it out of there. It wasn't something that defined Chris and it's unfortunate that it's been dwelled on as much as it has. You know, certain people are willing to do anything they can to win a lawsuit and — well, I'll just leave it at that. Or I might find myself getting sued alongside him."