A US jury has sentenced Army psychiatrist Nidal Hasan to death for killing 13 people during the 2009 shooting rampage at Fort Hood in Texas.
The US-born Muslim said the attack on unarmed soldiers was motivated by a desire to protect insurgents fighting in Iraq and Afghanistan. He offered no defence in his trial.
The same jury that sentenced him to death found him guilty last week in the attack, which also wounded more than 30 people.
Hasan has said he acted to protect Islamic insurgents abroad from American aggression, and he never denied being the gunman. He acknowledged to the jury that he pulled the trigger in a crowded waiting room where troops were getting final medical checkups before deploying to Iraq and Afghanistan. Thireteen people were killed and more than 30 wounded. It was the worst ever attack on a US military base.
The same jurors who convicted Hasan last week had two options: agree unanimously that Hasan should die or watch the 42-year-old get an automatic sentence of life in prison with no chance of parole.
Hasan could become the first US soldier executed in more than half a century. But because the military justice system requires a lengthy appeals process, years or even decades could pass before he is put to death.
The lead prosecutor assured jurors that Hasan would "never be a martyr" despite his attempt to tie the attack to religion. "He is a criminal. He is a cold-blooded murderer," Col. Mike Mulligan said in his final plea for a rare military death sentence.
For nearly four years, the federal government has sought to execute Hasan, believing that any sentence short of a lethal injection would deny justice to the families of the dead and the survivors.
During the trial, Hasan leaked documents to journalists that revealed him telling military mental health workers in 2010 that he could "still be a martyr" if executed. All but one of the dead were soldiers, including a pregnant private who curled on the floor and pleaded for her baby's life.
The attack ended only when Hasan was shot in the back by an officer responding to the shooting. Hasan is now paralysed from the waist down.