When Eddie Routh, 25, arrived at his sister's Midlothian home, he reportedly confessed to a double homicide Saturday.

He was driving a pickup truck, his sister had never seen before, according to an affidavit for his arrest. Routh, a military veteran who was reportedly suffering from mental illness, told his sister he had, "traded his soul for a new truck."

If the charges against Routh are true, that trade was made on the lives of two men - a decorated Navy SEAL and his neighbor who was reportedly ex-Army. Not much is known about what drove Routh to allegedly murder Chris Kyle, 38, and Chad Littlefield, 35, at Rough Creek Lodge Saturday afternoon. But officials do know the suspect and the two victims went to the hunting resort together and were seen approaching the facility's hunting range just after 3 p.m.

The victims were found unconscious and covered in blood by an employee of the sprawling Erath County ranch - located a short distance from the Somervell County line - around 5 p.m., Erath County Sheriff Tommy Bryant said.

"The guide went to the lodge and called 911," Erath County Sheriff Tommy Bryant said. "The victims where deceased when a deputy arrived."

Kyle, a former Navy SEAL, is credited as being the deadliest sniper in United States history. He co-authored a best-selling autobiography, entitled "American Sniper." He served four tours of duty in Iraq, where he was given the nickname "The Devil of Ramadi" by insurgents. News of his murder spread across the Internet Saturday even before his identity was confirmed by police.

Few details are known about Littlefield - reportedly Kyle's neighbor - who resided in Midlothian. Officials said he was a business owner who served a stint in the Army.

The murder suspect, a Lancaster resident, is reportedly a former Marine who served a four-year stint including time in Iraq and Afghanistan. He was arrested on murder warrants for the double slaying about four hours after his alleged victims were discovered.

Law enforcement officials held a press conference at the Erath County Sheriff's Office Sunday, mere steps from where Routh was being held on a $3 million bond.

Erath County District Attorney Alan Nash said Routh is being held on three warrants. He said initially, there was information that one victim was dead and a single murder warrant was signed. On confirmation of the second fatality, another warrant was issued. Nash said the pair justified the capital murder charge.

Following the shooting, Routh reportedly fled Rough Creek in Kyle's vehicle. In the early hours of the investigation, an all points bulletin (APB) was sent out to law enforcement officials across the area, searching for the distinctly modified Ford pickup truck that had the logo of Craft International, a company owned and operated by Kyle that provides training to the military and law enforcement officials, in the back window. It was the truck his sister saw him driving.

After fleeing the scene, Routh allegedly admitted the killings to his sister and brother-in-law at their Midlothian home, according to Bryant, who said the couple immediately called 911.

While Routh reportedly told his sister he wanted to get to Oklahoma in an effort to evade Texas authorities, the pursuit led police to the suspect's residence in Lancaster where he was found around 8 p.m.

There was contact between Routh and Lancaster police at that time, but he was not immediately arrested. He at some point fled the home and was later apprehended when police spiked his tires while he was traveling along Interstate 35 at about 9 p.m.

"The vehicle was stopped, and Routh was apprehended without incident," Bryant said.

Captain Jason Upshaw said the murder weapon appears to be a semi-automatic handgun, found at Routh's residence, but officials are waiting on a ballistics report.

Upshaw also said they are waiting on autopsy findings to reveal exactly how many times the victims were shot.

An affidavit requesting a warrant for Routh's arrest, signed by Investigator Randy Fowler, said both victims were obviously deceased, having suffered multiple gunshot wounds. It also states there were numerous firearms at the scene, including semi-automatic rifles, semi-automatic handguns and revolvers.

While it is not clear what led to the slayings, Routh reportedly suffers from mental illness.

Stephenville attorney Shay Isham has been appointed to represent him, and spoke with the Stephenville Empire-Tribune about his client's mental state after meeting with Routh early Monday.

"This is clearly going to be a mental health case," Isham said. "(Routh) was under the care of a VA hospital as recently as last month."

Isham said it was too early to comment on the case, but said the suspect was "guarded" during their visit.

"It was a one-sided conversation," Isham said. "My main concern now is getting him back on his medication."

Officials said Sunday those same mental concerns are believed to have brought the three men together at Rough Creek.

"There had been some mention that the suspect's mother may have reached out to Mr. Kyle to ask for help for her son," Bryant said. "We have an idea that they may have been at the shooting range for some sort of therapy."

Kyle was the co-founder of FITCO Cares, a non-profit organization with a mission of helping veterans fight PTSD through physical fitness.

In addition to Erath County officials, law enforcement personnel from Stephenville Police Department, Lancaster Police Department, Somervell County, Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) and Texas Department of Public Safety's Texas Rangers are involved in the investigation.

"We have two victims and one suspect in custody," Upshaw said at the Sunday press conference. "Now is when the work starts."

While he did not resist arrest, Routh has reportedly lashed out at jailers while in custody, according to Bryant.

"Jailers went to pick up his tray after feeding time Sunday, and he refused to hand it over," Bryant said. "They asked several times and he still refused, said they would have to come get it."

When guards entered Routh's cell, he became "more and more aggressive."

"He had his fist drawn back like he was ready to assault the jailers," Bryant said.

Officials tasered the suspect to subdue him and he was placed in a restraint chair where he remained Monday morning.

While individuals across the nation continued to question what motivated the murder of two American heroes, Nash said additional facts will be presented to the media and public through the court system. He said the criminal justice system is very restricted and officials will work to obtain justice for Kyle and Littlefield while at the same time guaranteeing due process for Routh.

"This is a sad day, we lost two American heroes," Upshaw added. "Our hearts and prayers go out to their families and loved ones."