As the trial progressed, those suspicions grew. The military called nearly 90 witnesses, but Hasan rested his case without calling a single person to testify in his defense and made no closing argument. Yet he leaked documents during the trial to journalists that revealed him telling military mental health workers that he could "still be a martyr" if executed.
Death sentences are rare in the military and trigger automatic appeals that take decades play out. Among the final barriers to execution is authorization from the president. No American soldier has been executed since 1961.
Hasan spent weeks planning the Nov. 5, 2009, attack. His preparation included buying the handgun and videotaping a sales clerk showing him how to change the magazine.
He later plunked down $10 at a gun range outside Austin and asked for pointers on how to reload with speed and precision. An instructor said he told Hasan to practice while watching TV or sitting on his couch with the lights off.
When the time came, Hasan stuffed paper towels in the pockets of his cargo pants to muffle the rattling of extra ammo and avoid arousing suspicion. Soldiers testified that Hasan's rapid reloading made it all but impossible to stop the shooting. Investigators recovered 146 shell casings inside the medical building and dozens more outside, where Hasan shot at the backs of soldiers fleeing toward the parking lot.
The first person to charge Hasan, a civilian doctor, was shot dead while wielding a chair. Another soldier who ran at him with a table was stopped upon being shot in the hand.
Chief Warrant Officer Christopher Royal saw an opening after hearing the distinct clicking of the gun's chamber emptying. But he slipped on a puddle of blood while starting a sprint toward Hasan. He was shot in the back.
Tight security blanketed the trial. The courthouse was made into a fortress insulated by a 20-foot cushion of blast-absorbing blockades, plus an outer perimeter of shipping containers stacked three high. A helicopter ferried Hasan back and forth each day. The small courtroom was guarded by soldiers carrying high-powered rifles.
In court, Hasan never played the role of an angry extremist. He didn't get agitated or raise his voice. He addressed Osborn as "ma'am" and occasionally whispered "thank you" when prosecutors, in accordance with the rules of admitting evidence, handed Hasan red pill bottles that rattled with bullet fragments removed from those who were shot.
His muted presence was a contrast to the spectacles staged by other unapologetic jihadists in U.S. courts. Terrorist conspirator Zacarias Moussaoui disrupted his 2006 sentencing for the Sept. 11 attacks multiple times with outbursts, was ejected several times and once proclaimed, "I am al-Qaida!"
Prosecutors never charged Hasan as a terrorist — an omission that still galls family members of the slain and survivors, some of whom have sued the U.S. government over missing the warning signs of Hasan's views before the attack.