4 February 2013 Last updated at 15:32 ET

Chris Kyle murder: Suspect Eddie Ray Routh subdued in jail

An Iraq war veteran charged with murdering an ex-US Navy Seal sniper has been restrained in his cell after becoming aggressive, say officials.

Texas jail guards said they used a stun gun on Eddie Ray Routh, 25, after he became belligerent and refused to hand back his food tray.

He is accused of shooting Chris Kyle, author of 2012 bestseller American Sniper, and another man at a gun range.

Mr Routh was reportedly suffering from post-traumatic stress disorder (PTSD).

Kyle, 38, is said to have been helping him deal with the condition.

Erath County Sheriff Tommy Bryant said guards had used the stun gun after Mr Routh appeared ready to attack them.

They had entered the suspect's solitary confinement cell because he had refused to return his food tray, added Sheriff Bryant.

Suicide watch

After using the stun gun once, prison officials put the accused in a chair that restrains the arms and legs. He is said to be on suicide watch after the incident.

Mr Routh has been charged on two counts of murder and is being held on $3m (£1.9m) bail.

The shootings occurred on Saturday afternoon at the Rough Creek Lodge range.

The gunman then fled in a pick-up truck belonging to one of the victims, local media reported.

A hunting guide found the bodies of Kyle and his neighbour, Chad Littlefield.

Sheriff Bryant said Mr Routh then travelled to his sister's home, telling her what had happened before leaving.

She called the police and Mr Routh was arrested several hours later near his home in Lancaster, Texas, more than 70 miles (110 km) from the crime scene.

Sheriff Bryant said the motive for the killings was unclear, but noted: "It's my understanding that the suspect may have been suffering from some type of mental illness from being in the military himself."

'The Devil'

Travis Cox, director of a non-profit organisation Kyle had helped found, told the Associated Press news agency that Mr Routh was suffering from PTSD and that Kyle and Littlefield were trying to help him.

"Chris died doing what filled his heart with passion - serving soldiers struggling with the fight to overcome PTSD," Mr Cox said.

Littlefield was Kyle's "work-out buddy" and volunteered his time with the veterans, Mr Cox said.

Scott McEwen, who co-authored the book with Kyle, said: "It just comes as a shock and it's staggering to think that after all Chris has been through, that this is how he meets his end, because there are so many ways he could have been killed."

Kyle, a former cowboy, is regarded as the most prolific sniper the US has ever seen.

Official Pentagon figures say he killed 160 people, but he estimated the total was 255.

According to military intelligence, he was nicknamed the Devil by Iraqi insurgents, who put a $20,000 (£13,000) bounty on his head.

"Every person I killed I strongly believe that they were bad," he told the BBC in an interview a year ago.

"When I do go face God there is going to be lots of things I will have to account for, but killing any of those people is not one of them."