Washington - An Iraq war veteran believed to be suffering from post-traumatic stress disorder has been charged with killing a former Navy Seal whose exploits in the same conflict were detailed in a best-selling book.
Chris Kyle, who wrote 'American Sniper: The Autobiography of the Most Lethal Sniper in US Military History', and a second man were shot dead at a firing range in Glen Rose, Texas on Saturday.
Kyle, aged 38, was credited with more than 150 confirmed kills during a decorated decade-long service career that included four tours in Iraq.
Since leaving the Seals, he had helped run a support group for struggling ex-military personnel.
His memoir recounted battle experiences in Iraq in the rebel strongholds of Ramadi and Fallujah, and he wrote that al-Qaeda militants whose comrades he had gunned down dubbed him "The Devil", and said they had put a bounty on his head.
The rebels of Iraq never did track Kyle down but he nevertheless died at the end of a gun in tragic circumstances, on American soil.
Captain Jason Upshaw of the Erath County Sheriff's Office told reporters on Sunday that Kyle and a friend had taken Eddie Routh, a US Marine who had also served in Iraq, to the shooting range.
Routh, aged 25, was formally charged on Sunday with two counts of capital murder in connection with the deaths.
"We lost two American heroes," Upshaw told reporters, noting that the weapon thought to have been used in the incident, a semi-automatic handgun, had been found at Routh's home.
Sheriff Tommy Bryant said Routh was believed to be suffering from "some type of mental illness", or post-traumatic stress disorder (PTSD).
The suspected shooter's mother is believed to have contacted the veterans support foundation that Kyle was involved with.
Kyle's death had earlier been confirmed by FITCO Cares, the group he helped start which worked with returning soldiers who had PTSD.
"My heart is breaking," said FITCO's director, Travis Cox, noting that the former sniper leaves a wife and two children.
"Chris died doing what he filled his heart with passion - serving soldiers struggling with the fight to overcome PTSD."
The US military confirmed on Sunday that Routh had seen active service with the Marines in Iraq, but that he was currently listed as a reserve.
The Dallas Morning News wrote that Kyle was awarded two Silver Stars and five Bronze Stars with Valour for his military service.
Kyle said in an interview with the daily about one year ago that he was born for the work of a military marksman and at the age of 24 he took that step.
"When I grew up, I only had two dreams. One was to be a cowboy and another was to be in the military. It wasn't exactly the Seals I was looking for at the time. I just wanted to go into the military and be the best."
The fatal shooting comes amid a raging and bitterly fought debate in the United States over gun control, after several massacres in which publicly available high-powered, military-style weapons have been used.
The issue of gun killings at the hands of people suffering from mental or emotional illness has figured prominently in such arguments, with calls for tighter background checks for gun owners.
In December, a mentally disturbed man killed 20 young children and six adults at the Sandy Hook elementary school in Newtown, Connecticut in a massacre that shocked the nation.
President Barack Obama has since put gun control on his legislative agenda with plans to ban assault rifles and high capacity magazines at its forefront, and on Monday he will travel to Minneapolis to begin a fresh push on the issue.
The measures, however, are up against fierce opposition from gun advocates, most notably the National Rifle Association, given that the right to bear arms is enshrined in the US constitution.