The Iraq War veteran charged with killing a former Navy SEAL sniper and his friend on a Texas shooting range told his sister that he "traded his soul for a new truck," according to an arrest affidavit released by a justice of the peace.

Eddie Ray Routh also said he wanted to drive to Oklahoma to avoid Texas authorities, according to an Erath County arrest warrant.

Erath County Sheriff's Capt. Jason Upshaw said Monday that Eddie Ray Routh drove to his sister's house in Midlothian after the shootings on Saturday and told her that he killed two people.

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On Sunday, Sheriff Tommy Bryant said Routh told his sister "what he had done." Bryant did not provide more information at the time.

Routh, a member of the Marine Corps Reserve, is being held at the Erath County Jail on $3 million bond. Routh is being held in isolation and a stun gun was used on him after he became combative over returning a dinner tray. According to Erath County Sheriff Tommy Bryant, Routh was placed on suicide watch.

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Murder of former Navy SEAL turns spotlight on veteran hunting and shooting clubs 

Ex-Navy SEAL sniper Chris Kyle died pursuing his passion

The former top Navy SEAL sniper who authorities say was killed at a Texas shooting range was devoted to maintaining camaraderie and helping his fellow veterans find their way after leaving active duty. 

Chris Kyle, author of the best-selling book "American Sniper," and his friend Chad Littlefield apparently were doing just that Saturday when, officials say, they were shot and killed by former Marine Eddie Ray Routh. 

Kyle, 38, had left the Navy in 2009 after four tours of duty in Iraq, where he earned a reputation as one of the military's most lethal snipers. But he quickly found a way to maintain contact with his fellow veterans and pass on what had helped him work through his own struggles. By late 2011, he filed the paperwork to establish the nonprofit FITCO Cares, which received its nonprofit status the following spring, said FITCO director Travis Cox. 

"Chris struggled with some things," Cox said. "He'd been through a lot and he handled it with grace, but yeah he did struggle with some things. And he found a healthy outlet and was proactive in his approach to deal with those issues and wanted to help spread his healing, what worked for him, to others. And that's what he died doing." 

For Kyle that healthy outlet was exercise. At the heart of FITCO was giving in-home fitness equipment to physically and emotionally wounded veterans, as well as families who had lost a veteran, Cox said. 

Littlefield, a 35-year-old friend and neighbor, was Kyle's "workout buddy," and also volunteered his time to work with veterans, Cox said. He was married and had children as well. 

"He's a very gentle, sweet-hearted man, just a great man, kind of quiet," Cox said of Littlefield. "He just really cared. ... He wanted to do whatever he could to help veterans and help see that vision of serving others that Chris had. He shared that vision with all of us. He was a great man." 

Cox said he understood that Kyle and Littlefield were helping Routh work through his own PTSD, but that he did not know how they came into contact. He said it was not a FITCO session. 

Erath County Sheriff Tommy Bryant on Sunday offered a similar description of the situation. 

"It's my understanding that the suspect may have been suffering from some type of mental illness from being in the military himself," he said of Routh. 

He said Routh's mother may have reached out to Kyle for help with her son. 

"We kind of have an idea that maybe that's why they were at the range for some type of therapy that Mr. Kyle assists people with," Bryant said. 

Bryant didn't know whether Routh was on any medication or whether he had been diagnosed with post-traumatic stress disorder. 

Authorities say the three men arrived at the Rough Creek Lodge southwest of Fort Worth around 3:15 p.m. Saturday. A hunting guide discovered the bodies of Kyle and Littlefield around 5 p.m. and called 911. 

Routh allegedly left in Kyle's pickup and went to his sister's in Midlothian. He told what he had done and left. She called police and Routh was eventually found at his home in Lancaster. After a short pursuit he was arrested. 

Routh was being held on $3 million bail in the Erath County Jail. Authorities said they believed he had requested a court-appointed attorney. Calls to his home were not answered Sunday. 

Kyle was also president of a security training firm Craft International. Craft had scheduled a $2,950-per-person civilian training event at Rough Creek Lodge called the "Rough Creek Shoot Out!" for March 1-3. The price included lodging, meals and shooting instruction. Kyle was scheduled to teach the first class, called "precision rifle." 

But the work with veterans through FITCO was Kyle's passion, Cox said. 

FITCO Cares offered life coaching for veterans, a daily support group and weekly group counseling. Sometimes veterans in other states would video conference in to counseling sessions, Cox said. 

Kyle was always recognized at events, but would deflect attention to other veterans, quickly introducing and praising those around him. 

"That camaraderie is usually missed once the veteran gets out of the military," said Cox, himself a former Marine sniper. "The authentic relationships that you develop in the military, especially overseas and in combat are some of the most meaningful, authentic relationships that one can have and it's missed. And so we tried to create a means through this group of veterans that can gather and talk about things that they're dealing with." 

"He (Kyle) didn't have any fear at all as far as working with an extreme case," Cox said. "Just like in combat he would take it on head on and do whatever he could to give these guys assistance. There was no fear in helping anyone that may have an extreme case. He was willing to help anyone in need."