* Suspect visited sister after slayings
* "He's all crazy," sister says in 911 call (Adds information about 911 call, changes byline, adds dateline)
By Marice Richter and Jim Forsyth
DALLAS, Feb 5 (Reuters) - The suspect accused of shooting dead former Navy SEAL sniper Chris Kyle and another man stole a vehicle from the scene and told his sister "I traded my soul for a new truck," investigators said on Tuesday.
Eddie Ray Routh is being held on one count of capital murder and two counts of murder in the slayings on Saturday of Kyle and Chad Littlefield.
Investigators said that shortly after the shooting Routh visited his sister, Laura Blevins, who said on a 911 emergency call released on Tuesday that the visit left her scared.
"Listen, my brother just came by here and told me he committed a murder," Blevins said in a call released by police in Midlothian, Texas. "I'm terrified for my life because I don't know if he is going to come back here."
Blevins, who could be heard herding others into a car to go to the police department, said she didn't know if her brother was telling the truth.
"He's all crazy, he's ... psychotic," she said. "I don't know if he's on drugs or not. My husband is going to talk to you because I'm so nervous."
The husband, who was not identified on the recording, said on the call that Routh, an Iraq war veteran, had recently been diagnosed with post-traumatic stress disorder.
"He got out of a mental hospital last week," Blevins' husband said of Routh. The call ended when the couple reached the police department.
Routh, 25, of Lancaster, Texas, served in the Marines from 2006 to 2010, including a tour in Iraq, and that fact has put attention on the psychological wounds of war. The new evidence about the truck, which first came to light on Monday, suggests robbery could have formed part of the motive.
Kyle, author of the book "American Sniper," was credited with more than 150 killings as a sniper for U.S. forces in Iraq and had been working with military veterans recovering from physical and emotional injuries, sometimes inviting them to the shooting range.
Randy Fowler, an investigator with the Erath County Sheriff's Department in Texas, wrote in the affidavit that Routh drove to his sister's home in Midlothian, about 50 miles (80 km) from the gun range where the shooting took place, shortly after the incident.
Routh was driving what his sister described as a "big dark or black Ford F-250 pickup that she had never seen before," Fowler said in the affidavit.
"It substantiated Routh's claim that he had murdered Chris Kyle and his friend, and he told the Blevinses that he had killed Kyle and that he had 'traded his soul for a new truck,'" Fowler wrote.
Routh was later arrested at his home in Lancaster, Texas, south of Dallas, after leading officials on a brief police chase while he was at the wheel of the truck, which has been identified as the one that Kyle, Routh, and Kyle's friend Littlefield drove to the shooting range earlier that day.
Two employees of the Rough Creek Lodge shooting range "found Chris and Chad lying on the ground covered in blood" about 1-1/2 hours after the trio arrived at the site, the affidavit said.
Routh's sister advised her brother to turn himself in, but Routh said he wanted to get to Oklahoma to avoid Texas authorities, the affidavit said.
Twice in recent months Routh was taken to a mental hospital after behaving erratically, according to police reports from Dallas and Lancaster.
Dallas television station KTVT reported that Lancaster police took Routh to a mental hospital in September after family members told officers he was threatening to kill himself during an argument with his father.
KTVT quoted Routh's relatives saying they believed he was a victim of the government's inability to provide the mental health treatment he needed for the emotional problems he suffered in combat.
Authorities have not said Routh specifically suffered from post-traumatic stress, a severe anxiety disorder caused by witnessing or participating in traumatic events, but the killings renewed the focus on PTSD among veterans.
About 30 percent of returning Iraq and Afghanistan war veterans suffered from some form of post-traumatic stress, the Department of Veterans Affairs estimated in a report released last year.
Kyle, who served four combat tours of duty in Iraq, won two Silver Stars and five Bronze Stars for bravery, according to his book, which covers his military service from 1999 to 2009. (Editing by Daniel Trotta, Edith Honan and Eric Beech)