Chris Kyle, a retired Navy SEAL and the U.S. military's most lethal sniper, was fatally shot Saturday along with another man on the gun range of Rough Creek Lodge, a posh resort just west of Glen Rose, Erath County Sheriff Tommy Bryant said.

A suspect was arrested about five hours later in Lancaster, southeast of Dallas, more than 70 miles from the scene, Bryant said.

The suspect, identified as Eddie Ray Routh, 25, was pursued to a house in Lancaster by officers, including a local SWAT team. Routh tried to flee in a vehicle but was stopped about 9 p.m. after spikes were laid across a road, Bryant said.

"The suspect has been caught and is in custody in Lancaster," he said. Erath County sheriff's investigators and Texas Rangers were securing a capital murder warrant, he said.

Witnesses told sheriff's investigators that the gunman opened fire on the two men around 3:30 p.m., then fled in a pickup belonging to one of the victims. The Sheriff's Department didn't get a call until around 6 p.m.

Rough Creek Lodge is 77 miles southwest of Fort Worth between Glen Rose and Hico.

The motive for the shootings remains unclear, Bryant said. "Not a clue, absolutely no idea."

WFAA/Channel 8 quoted unnamed sources as saying that Kyle, who lived in Midlothian, and a neighbor had taken Routh on an outing to help him deal with post-traumatic stress disorder. Routh turned on the men and shot them in the back, the report said.

The sheriff said he could not confirm how the victims were shot.

In January 2012, the Cleburne Times-Review reported that Routh, of Lancaster, was arrested in Johnson County on suspicion of driving while intoxicated. Public records show that Routh previously lived in Camp LeJeune, N.C., a major Marine base.

Kyle, 38, who is survived by a wife and two children, was the author of American Sniper, a 2012 autobiography.