Gunman kills 12 at U.S. Army base

"Thanks to the quick reaction of several soldiers, they were able to close off the doors to that auditorium where there were some 600 people inside," Cone said.

"As horrible as this was, I think it could have been much worse," Cone said.

Cone said soldiers as a rule do not carry weapons on the base. Military police and security guards are armed.

SUSPECT SAID TO BE UPSET ABOUT DEPLOYMENT

A cousin of the suspected shooter, Nader Hasan, told Fox News that he had been ordered to serve a term in Iraq and had been resisting such a deployment.

Hasan said his cousin was a U.S.-born Muslim who had joined the military from high school. He had served as a psychiatrist at the Walter Reed Army Medical Centre in Washington, D.C., which treats many badly wounded troops.

"He was a psychiatrist at Walter Reed dealing with the people coming back and ... trying to help them with their trauma," he said.

He said his cousin had been transferred to Fort Hood in April months ago and was very reluctant to be deployed to Iraq. "We've known over the last five years that was probably his worst nightmare," he said.

The incident raised new questions about the toll that six years of continuous fighting in Iraq and nearly eight years of fighting in Afghanistan have taken on the U.S. military and on individual soldiers, many of whom have been on several combat tours.

U.S. President Barack Obama, speaking in Washington, called the event a "horrific outburst of violence" and promised "answers to every single question about this horrible incident."