Maj. Nidal Malik Hasan could face the death penalty if convicted.

Army officials said that they believe that Hasan acted alone when he jumped on a table with two handguns last week, shouted "Allahu akbar!" - God is the greatest - and opened fire. The dead included at least three other mental- health professionals; 29 others were injured.

Additional charges were possible, said Chris Grey, spokesman for the Army Criminal Investigation Command.

Meanwhile, Obama ordered a review of all intelligence related to Hasan to determine whether it had been properly shared and acted upon within the government. John Brennan, assistant to the president for homeland security and counterterrorism, will oversee the review.

Members of Congress are pressing for a full investigation into why Hasan was not detected and stopped. A Senate hearing on Hasan is scheduled for next week.

A joint terrorism task force overseen by the FBI learned late last year of Hasan's repeated contact with a radical Muslim cleric who encouraged Muslims to kill U.S. troops in Iraq. The FBI said that the task force did not refer early information about Hasan to superiors because it concluded that he wasn't linked to terrorism.

Hasan was charged in the hospital without his lawyers present, said John Galligan, his civilian attorney.

Months before the shootings, doctors and staff overseeing Hasan's training reported viewing him at times as belligerent, defensive and argumentative in his frequent discussions of his Muslim faith, according to a military official familiar with several group discussions about Hasan. The official was not authorized to speak publicly about the meetings, and spoke on condition of anonymity.

Hasan was characterized as a mediocre student and lazy worker, which concerned the doctors and staff at Walter Reed Army Medical Center and the Uniformed Services University of the Health Sciences, a military medical school in Bethesda, Md., the official said.