(CNN) -- Authorities say they were forced to use a Taser and physically restrain the suspect accused of gunning down a well known former Navy SEAL and another veteran over the weekend.
Eddie Ray Routh was immobilized with a Taser strike after he refused to give up a spork and dinner tray and became aggressive with guards in his jail cell Sunday night, Erath County Sheriff Tommy Bryant said Monday.
Routh, 25, faces capital murder charges for allegedly slaying Chris Kyle, the author of the best-selling "American Sniper" book, and Chad Littlefield, also a veteran.
Their shooting deaths at a Texas hunting range Saturday afternoon sparked an outpouring of support for their families, praise for their work and outrage over the killing.
Thousands pledged to toast to Kyle and Littlefield Monday night, and hundreds expressed condolences on Kyle's Facebook fan page.
The administrator of that page posted a tribute to Littlefield, saying: "Chad felt deeply about the values of family, compassion, friendship and loyalty, and was equally as passionate about his love of God and country."
Routh is on suicide watch and under 24-hour camera surveillance, Bryant said Monday.
Since the suspect's arrest Saturday, multiple threats have been made against his life, Bryant said. Some of those, the sheriff believes, came from military veterans who are upset over the killings.
Because of the threats, Routh will likely remain at the jail for his pre-trial hearing rather than going to a courthouse, due to security concerns, Bryant said.
Routh's family members could not be reached immediately for comment, and no attorney has made a public statement on his behalf.
Kyle and Littlefield were gunned down Saturday afternoon on the grounds of the expansive Rough Creek Lodge and Resort in Glen Rose, Texas, southwest of Fort Worth, law enforcement officials said.
Authorities arrested Routh about four hours later, and 90 miles from where those two men's bodies were found by a hunting guide.
Kyle, Littlefield and Routh arrived together at the 3:15 p.m. (4:15 p.m. ET) Saturday and proceeding to a shooting range within the resort's 11,000 acres, Bryant told reporters Sunday.
Kyle and Littlefield were friends, associates said. Details about their relationship with Routh were not immediately clear.
A statement from Craft International, a company Kyle founded, described the suspect as "a troubled veteran whom they were trying to help."
So who is Eddie Ray Routh?
The sheriff said that Routh spent four years in the Marines. He is believed to have left the service in 2010, according to a U.S. military official who spoke on condition of anonymity because of the sensitivity of the situation. The official did not have information on where Routh served or whether he took part in combat.
Public records show Routh previously lived at Camp Lejeune Marine base in North Carolina, though his latest address was in Lancaster, Texas.
At the time of shooting, he was unemployed. Bryant said that Routh's mother, a longtime schoolteacher, "may have reached out to Mr. Kyle to try and help her son."
Kyle had reached out to other veterans.
He helped established the FITCO Cares foundation, a charity that helps U.S. war vets "who have survived combat but are still fighting to survive post-traumatic stress disorder," the group's website said.
Standing 6 feet, 2 inches tall and weighing a muscular 220 pounds, Kyle developed a deadly reputation in Iraq, prompting insurgents to put a bounty on his head, according to his autobiography.
Kyle expressed no regrets about any of the 160 people he claimed he killed as a Navy SEAL sniper during his five combat tours in Iraq.
When Kyle's military career ended after a decade, he joined other former SEALs to start Craft International, a security company with the motto "Despite what your momma told you, Violence does solve problems."
He also became a best-selling author, a reality TV personality, a supporter of fellow vets suffering from post-traumatic stress syndrome, an avid hunter and an outspoken opponent of gun control.