Col Dr Steven Braverman describes Major Nidal Malik Hasan and his work
A US major believed to have killed 13 people in a gun attack at a Texas army base was due to be deployed soon to Afghanistan, a military official said.
Maj Nidal Malik Hasan, 39, a US-born Muslim, opened fire on fellow soldiers at Fort Hood on Thursday.
Relatives of the army psychiatrist said he had strongly opposed his deployment and had wanted to leave the army.
US officials said investigations into what prompted the attack had continued through the night.
Early on Friday the commander of the Fort Hood base, Lt Gen Robert Cone, told NBC News that, according to eyewitnesses, the gunman had shouted the Arabic phrase "Allahu Akbar!" [God is great] before opening fire.
Military officials said 12 soldiers and one civilian had been killed.
MAJOR NIDAL MALIK HASAN
Born in US to Palestinian parents
Joined the army and trained to be a psychiatrist
Treated soldiers returning from combat zones
Described as a devout Muslim
Said to have been unhappy about imminent overseas deployment
Surveillance video showed he was wearing religious attire on the day of the shooting.
A fellow Fort Hood soldier told the BBC that the incident could put pressure on Muslim American soldiers.
"It kind of puts a negative light on them and makes people distrust them because everybody is going to look at them [and think]: 'Well, you're probably going to pull something like this'," the soldier said. "And it's a sad fact that that will happen."
The New York Times said the FBI had been investigating internet postings by a man called Nidal Hasan that appeared to back suicide bombings - but said it was not clear whether it was the suspect.
Texas Governor Rick Perry ordered all flags in the state to fly at half-mast as a tribute to the victims.
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