(DALLAS) -- Former Navy SEAL Chris Kyle and his neighbor Chad Littlefield took former Marine Eddie Ray Routh to a Texas gun range to help him, but for some reason Routh allegedly turned his gun on his two mentors, killing them both, police said on Sunday.
ABC News affiliate WFAA-TV in Dallas reported that investigators said Routh, 25, was recovering from post traumatic stress disorder, but police on Sunday said they could not confirm that.
Routh, a corporal in the Marines from June 2006 to January 2010, was deployed to Iraq in 2007 and Haiti in 2010, according to the Pentagon. His current duty status is listed as reserve.
"Apparently Mr. Kyle works with people that are suffering from some issues that have been in the military and this shooter is possibly one of those people, that he had taken out to the range to mentor, to visit with, to help him, you know, that's all I can tell you," said Erath County Sheriff Tommy Bryant.
"Kind of have an idea that maybe that's why they were at the range, for some type of therapy that Mr. Kyle assists people with, and I don't know if it's called shooting therapy," Bryant said. "I don't have any idea but that's what little bit of information that we can gather so far."
Witnesses told police that Routh left the shooting scene in Kyle's pickup truck. He drove to his sister's home in Midlothian and when he allegedly told her and her husband that he had shot the two men, the couple called the police.
When investigators got there, Routh fled in another vehicle, but he was captured a short time later.
Routh was charged with two counts of capital murder and was being held Sunday at the Erath County Jail on $3 million bond.
Erath County Sheriff's spokesman Jason Upshaw said investigators have recovered the alleged murder weapon.
"Right now it appears that he used a semi-automatic handgun," Upshaw said.
Kyle, who had more than 150 confirmed kills as a sniper serving four tours in Iraq, is the author of the best-selling book American Sniper: The Autobiography of the Most Lethal Sniper in U.S. Military History.
He helped found FITCO Cares, an organization that provides at-home fitness equipment for emotionally and physically wounded veterans, and was described by those who knew him as tireless and giving in his efforts to help vets.
"We have lost more than we can replace. Chris was a patriot, a great father, and a true supporter of this country and its ideals. This is a tragedy for all of us. I send my deepest prayers and thoughts to his wife and two children," Scott McEwen, co-author of American Sniper, said in a statement to ABC News.
Remembering Kyle for the number of Iraqi insurgents he killed misstates his legacy, McEwen said.
"His legacy is not one of being the most lethal sniper in United States history," McEwen said. "In my opinion, his legacy is one of saving lives in a very difficult situation where Americans were going to be killed if he was not able to do his job."
Kyle, 38, served four tours in Iraq and was awarded two Silver Stars, five Bronze Stars with Valor, two Navy and Marine Corps Achievement Medals, and one Navy and Marine Corps Commendation.
From 1999 to 2009, Kyle recorded more than 150 sniper kills, the most in U.S. military history.
After leaving combat duty, Kyle became a chief instructor, training Naval Special Warfare Sniper and Counter-Sniper teams, and he authored the Naval Special Warfare Sniper Doctrine, the first Navy SEAL sniper manual. He left the Navy in 2009.
American Sniper, which was published last year by William Morrow, became a New York Times best seller.
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