A United States army investigator says many more people could have died in an attack at an army base in Texas, if not for the heroism of security forces at the scene.
Details have emerged of action taken by two police officers to confront the suspect, Major Nidal Malik Hasan.
Thirteen people died and 38 were wounded in the Fort Hood shooting on Thursday.
Sergeant Mark Todd has described kicking away Major Hasan's gun and cuffing him, after colleague Kimberly Munley shot him, reports the BBC.
Investigators seek motive
An initial search of Major Hasan's computer revealed no direct exchanges with known extremists, but US Army and FBI officials had yet to rule out possible links to terrorist groups, American media reported.
Earlier this year, the Federal Bureau of Investigation learned of internet postings by a man calling himself Nidal Hasan that expressed support for suicide bombings.
Investigators were not able to determine yet whether the writer and Major Hasan are the same person, but the details have fuelled concerns authorities may have missed warning signs before attack, AFP reports.
Neighbours reportedly said Major Hasan was in a rush when he gave away his belongings - including a Koran - shortly before the shooting spree.
A US-born Muslim of Palestinian heritage, the 39-year-old psychiatrist had voiced dismay over US wars in Islamic countries and was distraught that he was about to be sent to Afghanistan.
He reportedly said the US struggle against terror threats was a "war on Muslims," while his family alleged he was the target of prejudice and harassment over his Islamic faith.
Investigators are poring over evidence to determine if the shooter was motivated by Islamist political ideology or had snapped under the pressure of his job counseling soldiers traumatised by combat.
Major Hasan, who was shot four times, remains in a coma. He has been moved from a civilian hospital to a military one for security reasons.
Obama praises heroism
President Barack Obama led the nation in mourning Saturday, and sought to reassure a stunned military.
In his weekly address, Mr Obama praised the heroism of soldiers and civilians in their response to the deadly attack.
"Thursday's shooting was one of the most devastating ever committed on an American military base," he said.
"And yet, even as we saw the worst of human nature on full display, we also saw the best of America."
Mr Obama hailed the soldiers and civilians who rushed to help victims, tearing off bullet-riddled clothes to treat the injured and using blouses as tourniquets.
However, he warned against being hasty in assigning a motive to the killings.
The president ordered flags to fly at half-mast at the White House and federal buildings, as troops at home and abroad held a minute's silence to mourn the dead.
