HOUSTON — From his perch in hide-outs above battle-scarred Iraq, Chris Kyle earned a reputation as one of America’s deadliest military snipers. The Pentagon said his skills with a rifle so terrorized Iraqi insurgents during his four tours of duty that they nicknamed him the “Devil of Ramadi” and put a bounty on his head.

The insurgents never collected, and he returned home to become a best-selling author and a mentor to other veterans, sometimes taking them shooting at a gun range near his Texas home as a kind of therapy to salve battlefield scars, friends said. One such veteran was Eddie Ray Routh, a 25-year-old Marine who had served tours in Iraq and Haiti.

But on Saturday, far from a war zone, Mr. Routh turned on Mr. Kyle, 38, and a second man, Chad Littlefield, 35, shortly after they arrived at an exclusive shooting range near Glen Rose, Tex., about 50 miles southwest of Fort Worth, law enforcement authorities said Sunday. The officials said that for reasons that were still unclear, Mr. Routh shot and killed both men with a semiautomatic handgun before fleeing in a pickup truck belonging to Mr. Kyle.

“Chad and Chris had taken a veteran out to shoot to try to help him,” said Travis Cox, a friend of Mr. Kyle’s. “And they were killed.”