Eddie Ray Routh has been found guilty of the murder of American Sniper Chris Kyle and his friend Chad Littlefield by a Texas jury.
The judge sentenced Eddie Ray Routh to life in prison without parole; prosecutors had not sought the death penalty.
Eddie Ray Routh’s defense lawyers said the 27-year-old was psychotic at the time of the shootings two years ago.
But prosecutors said Eddie Ray Routh was aware of what he was doing when he gunned the pair down at a Texas gun range in 2013.
The former Navy Seal, who has the most recorded kills of any US sniper, was shot and killed along with Chad Littlefield at a rural shooting range south-west of Fort Worth.
Having retired from the military, Chris Kyle had been helping other veterans deal with combat-related stress and mental health issues.
On the day of the killings, Chris Kyle and Chad Littlefield took Eddie Ray Routh with them to go shooting after the defendant’s mother asked for help in dealing with her troubled son.
Eddie Ray Routh, who suffered from post-traumatic stress disorder, was under extreme mental distress and was convinced the two men would turn on him on the day of the killing, his lawyers argued.
The court also heard that Eddie Ray Routh was under the influence of marijuana and alcohol at the time of the shooting.
In addition, he had been prescribed anti-psychotic medication often used for schizophrenia, reported the Associated Press news agency.
Defense lawyers said Eddie Ray Routh had been mentally affected by the time he spent helping earthquake relief efforts in Haiti with the Marines in 2010.
He had pleaded not guilty to the charge of murder on grounds of insanity.
However, a psychologist testified for prosecutors that Eddie Ray Routh was not legally insane, but instead had a paranoid disorder made worse by his drink and cannabis abuse, according to the Associated Press.
As prosecutors had not sought the death penalty, the sentence of life imprisonment without parole was imposed automatically by the judge.
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