Seema Hakhu Kachru

Houston, Nov 7 (PTI) US military psychiatrist Major Nidal Malik Hasan, responsible for a horrific shooting spree that left 13 dead, was in coma and transferred from a civilian to an army hospital for security reasons, officials said.

Hasan is said to be in critical but stable condition, attached to a ventilator, while many of his victims are still fighting for their lives in hospitals. His comatose condition is frustrating attempts by investigators to work out the motive behind his killings.

"The military officer suspected in the shooting deaths of 13 people here was transferred from a civilian to a military hospital in part for security reasons," a military official said.

So far, the investigators are trying to unravel many unknowns about the man they say is responsible for the worst killing on a US military base, most of all his motive.