The FBI has found evidence linking al-Qaeda to the Royal Saudi Air Force trainee who killed three American sailors in a December attack at a naval base in Florida.

US Attorney General William Barr said the FBI found the evidence after cracking the trainee’s mobile phone encryption.

The shooter, Second Lieutenant Mohammed Saeed Alshamrani, 21, also wounded eight people before being killed by law enforcement during the December 6, 2019 attack.

He was on the base as part of a US Navy training program designed to foster links with foreign allies.

The Justice Department succeeded in unlocking the encryption on the shooter’s iPhone after Apple declined to do so, Barr told reporters on a conference call on Monday.

“The information from the phone has already proved invaluable,” Barr said.

Apple later disputed his version, saying it co-operated to the extent that its technology allowed.

In February, an audio recording purporting to be from the Islamist militant group al-Qaeda in the Arabian Peninsula (AQAP) claimed responsibility for the attack, but provided no evidence.

Prior to the shooting spree, the shooter posted criticism of US wars and quoted slain al-Qaeda leader Osama bin Laden on social media.