Eddie Ray Routh, the former Marine who is accused of killing American military sniper Chris Kyle and his friend Chad Littlefield Saturday, was Tasered and placed on suicide watch after trying to attack guards at the Erath County Jail in central Texas Sunday night, authorities said.

Police said Routh has given no indication of his motive for the killings, but they’re looking into the possibility that he suffers from post-traumatic stress disorder.

Kyle, 38, was a Navy SEAL who served four tours of duty in Iraq and was known as the “Devil of Ramadi” by Iraqi insurgents who placed a bounty on his life. He penned the best-selling memoir “American Sniper” upon returning home and became a mentor to other veterans, organizing a charity designed to counsel those afflicted with PTSD.   

Kyle and Littlefield had taken Routh to a shooting range when he allegedly shot them both with a semiautomatic pistol for reasons that remain unclear. There appeared to be no signs of struggle and Kyle and Littlefield appeared to be shooting at targets when they were killed. Police told ABC News they arrested Routh driving Kyle’s pickup truck after a short pursuit.

Routh will be charged with two counts of capital murder and is being held on $3 million bail. The symptoms of PTSD include feeling emotionally numb, hearing or seeing hallucinations, irritability or anger, being easily startled, and having flashbacks to the disturbing event that can last for minutes or even days.

It hasn’t been confirmed if Routh, who as a Marine served in Haiti, was diagnosed with the mental illness, but a jail official, speaking on the condition of anonymity, told ABC that Routh had to be placed in solitary confinement and strapped to a chair. Guards also used a Taser on him after Routh was “trying to attack them.”

The New York Times reported that investigators were still trying to decipher how the three men knew each other but were given an indication that Kyle was contacted by Routh’s family.

“The suspect’s mother was a schoolteachfor a long time,” said Sherriff Tommy Bryant of Earth County. “She may have reached out to Mr. Kyle to try and help 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."

The sherriff later said in a new conference, “They all went out there together in the same vehicle. The suspect may have been suffering from some kind of mental illness from being in the military.”