After two days of inquiry into the shootings, officials believe Major Nidal Malik Hasan, the US Army psychiatrist accused in the shootings, snapped under a welter of emotional, ideological and religious pressures, reports said yesterday.
Federal officials told The New York Times investigators had not ruled out the possibility that Major Hasan believed he was carrying out an extremist suicide mission.
But the investigators, working with behavioral experts, told the paper he probably suffered from emotional problems that were exacerbated by the tensions of his work with veterans of the wars in Iraq and Afghanistan who returned home with serious psychiatric problems.
Officials told the paper his counseling activities with the veterans appeared to have further fuelled his anger and hardened his increasingly militant views and extreme religious beliefs.
The US Army released an official list of the 13 people fatally shot at Fort Hood and said 16 victims were still being treated in hospitals, nine of them in intensive-care units.
Major Hasan, had been taken off a ventilator but also remained in intensive care in an army hospital in San Antonio. They would not confirm that he was speaking.
After interviewing more than 170 witnesses, including some of the wounded, the army remains convinced that the major acted alone, said Chris Grey, a spokesman for the army's Criminal Investigation Division. But he said the motive for Major Hasan's deadly rampage has not yet been determined.
Major Hasan was slated to deploy to Afghanistan late this month. He opened fire in an area where soldiers from 20 units were waiting to enter a processing center where they would receive dental and medical treatment before going overseas.
The two guns he allegedly used in the attack have been sent to an army CID lab in Atlanta. Army officials have said Major Hasan fired more than 100 rounds from at least one handgun during the rampage.
A police officer and mother of one has been hailed a heroine after it emerged she almost single handedly ended the massacre at America's biggest military base.
Kimberly Munley, 35, happened to be nearby, waiting for her squad car to get a tune-up, when she heard the commotion and raced to the scene, according to her boss, Chuck Medley, director of emergency services on base.
As she rounded a corner, she saw Major Hasan chasing a wounded soldier through an open courtyard. He looked as though he was trying to "finish off" the wounded soldier, Mr Medley said.