Jury selection began Monday for the trial of a man charged with murdering former Navy SEAL Chris Kyle, whose autobiography was adapted into the movie “American Sniper.”

Eddie Ray Routh, 27, is charged with murdering Kyle and his friend, Chad Littlefield, at a shooting range in Texas in 2013.

Routh has confessed to the killings, but his behavior at the time was reportedly erratic. His attorneys are expected to argue he was insane at the time of the murders, and that his post-traumatic stress disorder, contracted after his tour of duty in Iraq and relief efforts in Haiti, played a part in the killings, the Associated Press (AP) reported.

"He wasn't prepared for what he was doing out there," his father told the Daily Mail, talking about Routh’s experiences after the 2010 Haiti earthquake that left almost a quarter million dead. "Fishing hundreds of bodies — men, women, children — out of the ocean, piling them up and throwing them into mass graves."

However, reports have cast doubts on Routh’s experiences in Iraq and Haiti. Marine records show that Routh was attached to a Battalion based in Fallujah, while Routh’s father reportedly said his son guarded prisoners at an airbase over an hour’s drive away.

"I don't know why we would send an armorer to Balad ... when there are plenty of MPs [military police] who have the training to guard prisoners," Former Marine Haley Carter told AP. "The whole thing seems funky to me."

Reports also indicate that in Haiti, Routh’s unit helped distribute food, water and medical supplies, but never participated in burials.

District Attorney Alan Nash has indicated he will not seek death penalty. Routh faces life in prison without parole if convicted. Defense attorneys had previously asked for a change of location for the trial, which was refused. Motions to postpone the trial were also turned down.

Kyle, who reportedly has the U.S. military’s highest kill count at 160, is known for writing an autobiography that was later adapted into “American Sniper.” The movie, which covers events during Kyle’s tour of duty in Iraq, has grossed over $250 million since opening in January, and has been nominated for six Academy Awards, including Best Picture, news site UPI reported.

Routh’s defenders have argued that the timing of the movie could cloud the jury's decision, leading to an unfair trial. Judge Jason Cashon told jurors they could still serve if they had seen the movie, the Dallas Morning News reported.