Maj. Nidal Hasan showed no reaction after being found guilty last week by a military jury, which will now decide whether the Virginia-born Muslim who said he opened fire on unarmed soldiers at the Texas Army post to protect insurgents abroad should be executed.
Twelve of the dead were soldiers, including a pregnant private who pleaded for the unborn child's life. More than 30 others were wounded. Investigators collected more than 200 bullet casings at the site of the attack.
At the minimum, the 42-year-old Hasan will spend the rest of his life in prison.
"This is where members (of the jury) decide whether you will live or whether you will die," Col. Tara Osborn, the trial judge, told Hasan on Friday following his conviction.
She then again implored Hasan, who represented himself during the 14-day trial, to consider letting his standby attorneys take over for the sentencing phase. He declined.
Jurors deliberated for about seven hours before finding Hasan guilty on all counts. He gave them virtually no alternative, as he didn't present a defense or make a closing argument, and he only questioned three of the nearly 90 witnesses called by prosecutors.
His silence convinced his court-ordered standby attorneys that Hasan wants jurors to sentence him to death. Hasan told military mental health officials in 2010 that he could "still be a martyr" if he is executed.
The sentencing phase will be Hasan's last chance to say in court what he's spent the last four years telling the military, judges and journalists: that the killing of American soldiers preparing to deploy to Iraq and Afghanistan was necessary to protect Muslim insurgents.
Hasan was prohibited from making a "defense of others" strategy during the guilt or innocence phase of his trial, but he will have more latitude during the sentencing portion. This has led legal experts and his civilian lawyer, John Galligan, to believe that Hasan could put himself on the witness stand this week.
Osborn didn't ask Hasan whether he might testify following his conviction. But she did ask whether Hasan felt he had been subject to "illegal punishment" or been unfairly restricted since being put in custody after the shooting.
He told Osborn he wasn't ready to answer.
"I'm still working on that," Hasan said.
Prosecutors want Hasan to join just five other U.S. service members currently on military death row, and are planning to put more than a dozen grieving relatives on the witness stand. Three soldiers who survived being shot by Hasan but were left debilitated or unfit for service are also expected to testify.
But most will be widows, mothers, children and siblings of the slain, who are expected to tell a jury of 13 high-ranking military officers about their loves ones and describe the pain of living the last four years without them.
What they won't be allowed to talk about are their feelings toward Hasan or what punishment they think he deserves.
Osborn told military prosecutors Friday to make sure their witnesses understood what topics were out of bounds. She was also considering excluding some family photos that could be considered duplicative, such as two different pictures of a victim in uniform.
"I understand the family members have memories of their loved ones," Osborn said. "But that's not part of the ruling I must make in a court of law."
Jurors must be unanimous to sentence him to death.
No American soldier has been executed since 1961. Many military death row inmates have had their sentences overturned on appeal, which are automatic when jurors vote for the death penalty. The U.S. president must eventually approve a military death sentence.
Associated Press writers Will Weissert and Paul J. Weber contributed to this report.