WASHINGTON — Federal investigators found cellphone evidence that links Al Qaeda to last year’s deadly shooting at a United States military base in Pensacola, Fla., according to two American officials briefed on the investigation.
The F.B.I. found that the gunman, Second Lt. Mohammed Saeed Alshamrani, a Saudi Air Force cadet training with the American military, had communicated with a Qaeda operative who had encouraged the attacks, according to the two officials, who were not authorized to speak about it publicly ahead of an 11 a.m. news conference by Attorney General William P. Barr.
The F.B.I. uncovered the links after recently bypassing the security features on at least one of Mr. Alshamrani’s two iPhones without help from Apple, according to the officials. They would not say what methods the investigators used to access the phones, but the move is likely to ease for now tensions between Apple and law enforcement officials who have demanded access to encrypted devices to investigate crimes.
It was not clear whether the Qaeda operative directed Mr. Alshamrani to carry out the December shooting, which killed three sailors and wounded eight people. In an audio recording earlier this year, the leader of Al Qaeda in the Arabian Peninsula claimed that his group directed a Saudi military officer to carry out the shooting.
But Mr. Alshamrani was in touch over time with the Qaeda branch, including its leadership at times, up to the attack, according to one of the officials, who said that Mr. Alshamrani’s ties to the group went beyond simply being inspired to act based on watching YouTube videos or reading extremist propaganda.
Mr. Alshamrani paused to fire at his iPhone during a firefight with security officers and he was found with a second, badly damaged phone that the Saudi destroyed, leading investigators to conclude that the devices held important data. But in January, Apple refused a Justice Department request to help open the iPhones, setting off fears that the government would seek a court order to force the company to comply.
The department said that it sought Apple’s help in opening the phones only after other agencies, foreign governments and third-party technology vendors had failed, and it accused the company of slowing the investigation and allowing leads to go cold.
The Justice Department and the F.B.I. declined to comment. CNN first reported investigators’ discovery of the links between Mr. Alshamrani and Al Qaeda.
Mr. Barr in January designated the shooting an act of terrorism. The night before the attack, Mr. Alshamrani had showed videos of mass shootings to guests at a dinner party, and he had posted anti-American, anti-Israeli and jihadist social media messages.
Three weeks later, Qassim al-Rimi, the leader of Al Qaeda in the Arabian Peninsula, said that his group directed Mr. Alshamrani to commit the murders in Pensacola. Mr. al-Rimi had a copy of what he said was Mr. Alshamrani’s will and messages that seemed to show the gunman had been in contact with the Yemeni-based group.
Soon after the recorded message was released, the United States confirmed that it had killed Mr. al-Rimi in a drone attack, a major blow to one of Qaeda’s last, vibrant branches.
While the F.B.I. has spent the last few years primarily trying to thwart international terrorism inspired by the Islamic State, Christopher A. Wray, the director of the F.B.I., said that Al Qaeda remains a potent threat. Mr. Wray told lawmakers last year that the group still wishes to conduct “large-scale, spectacular attacks.”
“Al Qaeda is more likely to focus on building its international affiliates and supporting small-scale, readily achievable attacks,” Mr. Wray said in testimony to the House Homeland Security Committee in October. “Simultaneously, over the last year, propaganda from Al Qaeda leaders seeks to inspire individuals to conduct their own attacks in the U.S. and the West.”
U.S. counterterrorism efforts have degraded the capabilities of Al Qaeda in Yemen and the Pakistan-Afghanistan region but the Pensacola shooting still shows the group’s ideology can inspire attacks. In 2016, authorities warned of a vague Qaeda threat.
Even though the casualty count was relatively low by Qaeda standards, simply “pulling off a successful attack on U.S. soil can provide Al Qaeda and its affiliates with a momentum boost and allow the group bragging rights over the Islamic State, which is important in terms of recruitment, prestige, and propaganda,” Colin P. Clarke, a senior fellow at the Soufan Center, a New York-based research organization, said in an email on Monday.
Even though the gunman was thought to operate alone, the government expelled 21 other Saudi students who were training with the American military, some of whom had links to extremist movements. After announcing the expulsions, Mr. Barr said that the Saudi government had cooperated fully with the investigation.
Saudi Arabia has a complicated relationship with Yemen, where it has been embroiled in a lethal, yearslong military battle to end Iranian influence there. Amid the airstrikes, Isis and Al Qaeda in the Arabian Peninsula have seized territory and carried out their own deadly attacks.
Mr. Alshamrani’s ability to train on the base as part of the U.S. military raises a host of thorny issues, including how the Defense Department screens potential recruits from Saudi Arabia.
Investigators believe that Mr. Alshamrani may have been under the influence of extremists at least since 2015, two years before he came to the United States and started strike-fighter training with the military.
The shooting also reignited the debate about when a technology company should be expected to help the government obtain information from encrypted messaging apps that can only be found if you can bypass the password and other security features. Apple routinely gives law enforcement lawful access to information that its users store in their iCloud accounts.
Though it was not clear how the F.B.I. got into Mr. Alshamrani’s iPhones, there are indications that Apple’s security is not as uncrackable as it used to be.
Last week, Zerodium — a company that acquires and sells weaknesses in smartphone encryption to American agencies to hack into those devices — announced it has a surplus of such exploits for Apple’s iOS mobile operating system.
The firm’s claims undermine the Justice Department’s and the F.B.I.’s assertions that Apple’s security is preventing lawful interception of data collection, especially on older model phones. Mr. Alshamrani had an iPhone 7 and an iPhone 5.
But Mr. Barr has maintained one of the department’s “highest priorities” is to find a way to get technology companies to help law enforcement gain lawful access to encrypted technology.
Nicole Perlroth and Eric Schmitt contributed reporting.