Hasan never denied being the gunman and has said the attack on unarmed soldiers was motivated by a desire to protect Muslim insurgents fighting in Iraq and Afghanistan.
Because he did not dispute the allegations, the trial has been primarily a pursuit of the death penalty.
The same jury that sentenced him to death Wednesday also found him guilty last week in the attack, which also wounded more than 30 people at the Texas military base.
Military prosecutors believed that any sentence short of death would deny.
Before an execution date is set, the sentence will face years, if not decades, of appeals.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
The Army psychiatrist who fatally shot 13 people at Fort Hood will "never be a martyr" and deserves to be executed despite his attempt to tie his attack on unarmed soldiers to religion, a prosecutor told jurors on Wednesday.
History was full of instances of death in the name of religion, but it would be "wrong and unsupportive" to tie Maj. Nidal Hasan's actions to a wider cause, Col. Mike Mulligan told jurors in his final plea for a rare military death sentence.
"He will not now and he will never be a martyr. He is a criminal. He is a cold blooded murderer," the lead prosecutor said. "This is not his gift to God. This is his debt to society. This is the cost of his murderous rampage."
Hasan, an American-born Muslim, has tried through court documents and leaks to the media to justify the November 2009 shooting rampage as necessary to protect Islamic and Taliban leaders from U.S. troops in Afghanistan and Iraq.
Hasan was never allowed to make those arguments to jurors, who convicted him last week for the attack that also wounded 30 people at the Texas military base. Still, Mulligan decided to answer those claims during the trial's penalty phase.
"It was conscious decision to commit murder to serve his own needs, his own wants," Mulligan said in his closing argument. "His attack by him was all about him. This is about his soul, for his soul he stole life from 13 others."
A few minutes after Mulligan finished, Hasan said he would give no closing argument — passing on his final chance to address jurors before they began deliberating his fate.
Hasan's choice marked a continuation of an absent defense strategy that he has used since his trial began three weeks ago.
The Army psychiatrist has been representing himself during his trial. But his behavior has only stoked suspicion that his ultimate goal was martyrdom, in the form of a death sentence that would allow him to fulfill what prosecutors have described as a "jihad duty" under his Islamic faith.
Hasan has done nothing to dissuade jurors from giving him a death sentence. Even when his standby lawyers pleaded in vain to argue on his behalf, he described them as "overzealous."
At the start of his trial he gave a brief opening statement, during which he said evidence would show he was the shooter and described himself as a soldier who had "switched sides." But he called no witnesses and didn't testify, and he questioned only three of the nearly 90 witnesses called by prosecutors before he was convicted. He also gave no closing statement.
During the sentencing phase of this trial, Hasan again presented no witnesses or evidence. And he questioned none of prosecutors' witnesses: dozens of widows, parents, children and other relatives of those killed who gave emotional testimony about their lives since the attack.
Prosecutors want Hasan to join just five other U.S. service members currently on military death row. That would require a unanimous decision by the jury of 13 military officers.
At minimum, the 42-year-old Hasan faces a sentence of life in prison.
Associated Press writer Will Weissert contributed to this report from Fort Hood.
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