(CNN) -- The 911 caller, her voice quavering, says she's terrified because of what her brother had just told her.
"He says that he killed two guys. They went out to a shooting range. Like, he's all crazy ..."
Those recorded words from the sister of Eddie Ray Routh gave Texas authorities one of their first indications Saturday of death at an isolated shooting range.
Routh, who was arrested hours after the call, is facing murder charges in the deaths of a military sniper and another military veteran.
Officials say Routh killed his fellow veterans on a gun range in a remote section of Rough Creek Lodge and Resort, which sprawls across 11,000 acres in Glen Rose, Texas, 90 minutes southwest of Dallas-Fort Worth.
The Saturday afternoon call from Routh's sister, Laura Blevins, came from her home in Midlothian, some 30 miles southeast of Fort Worth, after Routh, she said, had come to visit her and her husband.
"He's left now, but he told me that he's committed a murder, and I'm terrified for my life because I don't know if he's going to come back here," Blevins says in the call, her words spilling out in a torrent of worry. "I don't know if he's being honest with me."
Asked for detail, she says, "He says that he killed two guys. They went out to a shooting range. Like, he's all crazy. He's f****** psychotic. I'm sorry for my language. I don't know if he's on drugs or not."
In the recording of the call released Tuesday by the Midlothian Police Department, Blevins, saying she is nervous, hands the phone to her husband, Gaines.
"He said he killed two guys at a shooting range," Gaines Blevins says. "He took one of the trucks, like a dark blue or maybe black F-250. He drove off. I'm not sure where he is right now."
The man says that Routh told him he had two guns in the Ford pickup truck. Though the 25-year-old Routh had not threatened the couple, "he was talking kinda babble."
Asked whether Routh had been known to drink or take drugs, Gaines Blevins said, "Yeah, he's been known to drink in the past -- and smoke pot."
The speaker adds that Routh, an ex-Marine, had recently been diagnosed with post-traumatic stress disorder, "and he's been acting a little weird from that," and that he had left Green Oaks psychiatric hospital in Dallas the week before.
The release of the 911 tape came a day after Erath County Sheriff Tommy Bryant said Routh was under 24-hour surveillance on suicide watch in a central Texas jail.
Bryant has said Routh served for four years in the military, though it was unclear how much of that time, if any, was in combat zones.
Shay Isham, a lawyer appointed to represent Routh, has said his client had spent roughly the last two years in and out in Veteran Affairs medical facilities for treatment of mental issues.
Last September 2, Routh was crying, shirtless, shoeless and smelling of alcohol when police caught up with him walking the streets of his hometown of Lancaster, Texas.
His family didn't understand what the Marine veteran was going through, he told the officer, according to a police report.
He was taken then to a hospital for a mental evaluation and placed in protective custody after he had become angry that his father was going to sell his gun. His mother told police he had threatened to "blow his brains out."
This was, Bryant said, after Routh's mother "may have reached out to" one of the victims -- Chris Kyle, author of the best-selling book "American Sniper" -- "to try and help her son."
The suspect is "a troubled veteran whom they were trying to help," said Craft International, a company founded by Kyle, who had tried to help veterans with PTSD since he retired from the Navy in 2009.
Routh, Kyle and his friend, Chad Littlefield, entered the resort and headed toward a gun range at 3:15 p.m. (4:15 p.m. ET) Saturday, according to authorities.
Marcus Luttrell told CNN that Kyle, his friend, had gone to help Routh get "out of the house (and) blow off some steam."
Around 5 p.m. Saturday, a hunting guide alerted authorities Kyle's and Littlefield's bodies had been discovered "lying on the ground, covered in blood," according to an affidavit for the search warrant for Routh's house.
By then, Routh allegedly had taken off in Kyle's black Ford pickup, stopping first at his sister's house about 70 miles away.
Gaines Blevins said his brother-in-law said "he'd traded his soul for a new truck and that he murdered two people," the affidavit says. "He said they were out shooting target practice and he couldn't trust them so he killed them before they could kill him. He said he couldn't trust anyone anymore; everyone was out to get him."
Laura Blevins told her brother that if what he was saying was true, "he needed to turn hisself in," it adds.
But Routh set off again.
At about 8 p.m., police caught up with him near his home in Lancaster, about 15 miles south of Dallas, and took him into custody.
The motive for the killings was unclear.
Routh "is the only one that knows," Erath County Sheriff's Capt. Jason Upshaw told reporters on Sunday. "I don't know that we'll ever know."
CNN's Tom Watkins, Ed Lavandera, Josh Levs, Susan Candiotti, AnneClaire Stapleton, Barbara Starr, Emily Smith and Nick Valencia contributed to this report.