A U.S.-born citizen of Palestinian descent, Hasan had been scheduled to deploy to Afghanistan before the killings. Prosecutors hope to show that the devout Muslim had undergone a "progressive radicalization," giving presentations in defense of suicide bombings and about soldiers conflicted between military service and their religion when such conflicts result in crime.
Hasan did not want to deploy to fight against other Muslims and believed "that he had a jihad duty to kill as many soldiers as possible," said Col. Michael Mulligan, the lead prosecutor in the case.
Investigators found 146 spent shell casings in the room where the attack began, Mulligan said. Hasan carried two laser-sighted pistols and 420 rounds of ammunition, his pockets lined with paper towels to muffle the sounds of the magazines banging together, he said.
Internet searches on Hasan's computer used keywords like "terrorist killing," "innocent," "Quran," "fatwas" and "suicide bombings," Mulligan said.
Hasan told the panel in his opening statement, "We mujahedeen are trying to establish the perfect religion." But, he added, "I apologize for the mistakes I made in this endeavor."
The mujahedeen consider themselves warriors who defend the Islamic faith.
Hasan told his family he had been taunted after the al Qaeda attacks of September 11, 2001. Investigations that followed the killings found he had been communicating via e-mail with Anwar al-Awlaki, the Yemeni-American radical cleric killed by a U.S. drone attack in 2011.
The case was first set to begin in March 2012, but was delayed repeatedly, notably over a previous judge's unsuccessful demand that the beard Hasan has grown while in custody be forcibly shaved.