Mohammed Alshamrani also appeared to have posted criticism of US wars and quoted 9/11 mastermind Osama bin Laden on social media hours before the attack.
The 21-year-old airman, who was training at the Pensacola base, opened fire inside a classroom on Friday, killing three people and leaving at least eight others injured.
Two other students watched from the car, the official said, adding that ten Saudi students were being held at the base on Saturday.