US investigators believe the army doctor accused of killing 13 people in a shooting rampage at a Texas military base acted alone, but his motive for the massacre was unclear, officials said.
President Barack Obama will Tuesday attend a memorial service here to honour victims of the rampage at Fort Hood attributed to Muslim US army doctor Major Nidal Malik Hasan, who is also suspected of wounding 30 people.
"All evidence at this point indicates the suspect allegedly acted alone," Chris Grey, spokesman for the US Army criminal investigation division (CID), told reporters Saturday, adding that no motive had yet been established.
Criminal investigators were poring over evidence to determine if the alleged shooter - who survived gun wounds and is under guard at a military hospital in San Antonio, Texas - was motivated by Islamist ideology or had snapped under the pressure of his job counselling soldiers traumatised by combat.
According to The New York Times, investigators have tentatively concluded that Hasan was not part of a terrorist plot, but they have not ruled out the possibility that he believed he was carrying out an extremist suicide mission.
Citing unnamed officials, the newspaper said Sunday a search of Hasan's computer indicated he had logged on to websites that celebrated radical Islamic ideologies and exchanged email with like-minded people, some possibly overseas.
In addition, investigators believe he may have written inflammatory Internet postings that justified suicide attacks, though that has not been concretely established, The Times said. Late Friday, there were signs that Hasan's condition was improving. Colonel John Rossi, deputy commander of Fort Hood, told reporters that while the suspect was still in an intensive care unit, "he is no longer on ventilator." There was no word, however, on whether he was able to answer investigators' questions. Seventeen victims of Thursday's shooting remained hospitalised late Saturday, Rossi said.
A US-born Muslim of Palestinian heritage, Hasan had voiced dismay over US wars in Islamic countries and was distraught that he was about to be deployed 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.
Neighbours reportedly said Hasan, 39, was in a rush when he gave away his belongings - including a Koran - shortly before Thursday's bloody shooting spree.
"I'm not going to need them," he told one neighbour, Patricia Villa, according to The Times, handing over bags of vegetables, a mattress and clothing.
US officials and media reports highlighted Saturday the heroism of civilian police officer Kimberley Munley, 34, who rushed to the scene and gunned down the assailant, despite being wounded herself. According to Rossi, Munley underwent her second surgery early Saturday and was now listed in good condition.