A US military psychiatrist accused of killing 13 people in a shooting rampage at a key defence base has been moved to a San Antonio medical facility, the army's only level one trauma centre, as investigators searched for the motive behind the horrific incident.

Thirty-nine-year-old Major Nidal Malik Hasan, an American citizen of Jordanian descent, was captured after he was shot four times by a woman police officer following his shooting spree at Fort Hood military base in San Antonio near here yesterday.