FORT HOOD ? (UPDATE) Major Nidal Hasan, the shooter who killed 12 people at a Texas military base, is still alive and in hospital after undergoing surgery for his wounds, the base commander said Thursday.

"There was a single shooter that was shot multiple times at the scene," said Lieutenant General Bob Cone, "he was not killed as previously reported. He is currently in custody and in stable condition."

Cone said a "female civilian officer" was thought to be the first responder who shot the suspect.

The shooting took place as soldiers were awaiting medical and dental treatment at a processing center at Fort Hood for troops being deployed on missions to Iraq and Afghanistan, he said.

The "preponderance" of the victims was military personnel, but there were also two civilians involved, Cone added.

Further bloodshed was narrowly prevented when the gunman was apparently blocked from reaching a graduation ceremony attended by some 600 people, just meters away from the scene.

"Thanks to the quick reaction of several soldiers, they were able to close off the doors to that auditorium," Cone said.

After interviewing over 100 people at the scene investigators now appear to have ruled out the possibility that Hasan acted with an accomplice.

"There were initially three were held. All have been interviewed, and at this time we believe the evidence indicates it was a single shooter."