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 when Hasan was shot in the back by one of the officers responding to the shooting. He is paralyzed from the waist down and uses a wheelchair.
The sentencing phase is expected to include more testimony from survivors of the attack inside an Army medical center where soldiers were waiting in long lines to receive immunizations and medical clearance for deployment.
Hasan, who acted as his own attorney, began the trial by telling jurors he was the gunman. But he said little else over the next three weeks, which convinced his court-appointed standby lawyers that Hasan's only goal was to get a death sentence.
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 to 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.
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 evidence, handed Hasan red pill bottles that rattled with bullet fragments removed from those who were shot.
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.
Associated Press writers John Mone at Fort Hood and Ramit Plushnick-Masti in Houston contributed to this report.