Federal authorities said Monday that the Saudi Air Force officer who shot his fellow students at Pensacola Air Station in Florida last December was pushed by the al Qaeda terror group to carry out the attack, which they discovered after examining a cellphone that he tried to destroy.

Three people were killed and eight others were wounded when Mohammed Alshamrani — a Saudi Air Force officer here in the US for military training — opened fire in a classroom building on December 6.

Al Qaeda in the Arabian Peninsula (AQAP) claimed in an audio recording released in February that it directed him to carry out the attack. Five days after the recording was posted, the White House announced that the leader of the group, Qassim al-Rimi, was killed in a US attack.

FBI agents found two phones belonging to Alshamrani after the attack. They were especially eager to search one of them that investigators said he put on the floor and shot during his attack in an attempt to destroy any data it held. The Justice Department earlier this year strongly criticized Apple for refusing to help the FBI unlock the phone.

On Monday, Attorney General William Barr was expected to announced that the US was able to open the phone and recover much of the data it held without help from Apple.

US officials said from the beginning that they considered the attack an act of terrorism. They discovered that last September, Alshamrani posted this message on social media: “the countdown has started.” They say he also posted a string of anti-American, anti-Israeli and jihadist messages — the last one just two hours before the attack.