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The Saudi military trainee who killed three US sailors and wounded several others in a terror attack last year on a military base in Pensacola, Florida, was in touch with a suspected al Qaeda operative, according to multiple US officials briefed on the matter.

US investigators uncovered the al Qaeda connection after the FBI broke through the encryption protecting the Saudi attacker’s iPhones, the officials said. Attorney General William Barr and the FBI are expected to announce the finding Monday in a news conference.

Mohammed Alshamrani, a member of the Royal Saudi Air Force who had been training at Naval Air Station Pensacola, was killed by law enforcement during the attack.

A breakthrough on the shooter’s phone encryption for now temporarily disarms a standoff between the Justice Department and Apple over national security and the limits of encryption and privacy. The government has complained in recent years that stronger encryption, without the ability of law enforcement to get court-ordered access to data, endangers the public.

If Alshamrani was directed or trained by al Qaeda, it would mark the first time since 9/11 that a foreign terrorist organization had done so in a deadly attack in the US, according to New America, a think tank.

The Justice Department has previously called the attack an act of terrorism that was motivated by “jihadist ideology.” Alshamrani had made anti-American, anti-Israel and jihadi posts on social media, including one on the September 11 anniversary, that stated “the countdown has begun,” and another two hours before the attack that referenced the words of an al Qaeda cleric.

During a 15-minute shooting spree, Alshamrani shot at a photo of President Donald Trump as well as a former president. He also made statements during the attack that were critical of American servicemen overseas, the FBI has said.

Al Qaeda in the Arabian Peninsula, one of the deadliest branches of the terror group, had claimed responsibility for the Pensacola attack and said they were in touch with Alshamrani. In February, the White House announced that Qassim al-Rimi, the leader of the group, had been killed in an airstrike in Yemen.

No other co-conspirators have been charged in the shooting, and Barr said earlier this year that investigators did not find evidence that any of the shooter’s friends or fellow trainees from Saudi Arabia had advanced knowledge that he was going to attack the base.

Investigators had initially been unable to retrieve data stored on two iPhones belonging to the shooter, and they cited that hurdle in trying to complete their investigation of the attacker’s ideology and his radicalization. Justice Department and FBI officials said Apple had helped provide access to iCloud and other data from the shooter’s devices, but that breaking the phones’ encryption was key to retrieving more of Alshamrani’s communications before the attack.

In January, Barr criticized Apple for building their phones with encryption that usually blocks out even authorities with a search warrant, and urged the company to help investigators unlock the shooters’ devices.

Apple has said creating special access to its devices for the government was where it would draw the line, noting in January “there is no such thing as a backdoor just for the good guys. Backdoors can also be exploited by those who threaten our national security and the data security of our customers.”

A number of lethal terror attacks in the US have been inspired by a foreign terrorist organization, although none have been successfully directed by the groups since the 9/11 attacks that left nearly 3,000 people dead, according to a 2019 study by New America.

Al Qaeda thrived for years after 9/11, conducting deadly terror attacks in Madrid and across the Middle East, but was largely hollowed out under the Obama administration, which waged a campaign against the group’s core in Pakistan. Trump announced in September that Hamza bin Laden, the son of the late al Qaeda leader Osama bin Laden, had been “killed in a United States counterterrorism operation in the Afghanistan/Pakistan region.”