WASHINGTON (NEXSTAR) – The latest details on the investigation into last month’s deadly shooting at a Pensacola Naval base were revealed on Monday.

“This was an act of terrorism,” United States Attorney General William Barr said.

The Department of Justice and the FBI said the shooter posted anti-American, anti-Israeli and Jihadi messages on social media just hours before the attack.

They said the 21-year-old shooter acted alone when he killed three American service members and injured eight others on Dec. 6. He was a member of the Saudi military taking part in a U.S. training program.

“The Royal Saudi Air Force, which flies American-made aircraft, is an important military partner and has long had a training relationship with the United States,” Barr said.

During the investigation, Barr said 21 other Saudi trainees were found to have made derogatory posts about the U.S. on social media. Some also possessed child pornography.

All 21 are now removed from the training program and returning to their home country.

Barr said the next step in the investigation will be unlocking the shooter’s cell phone to examine its contents. But that is proving to be a challenge.

“So far, Apple has not given any substantive assistance,” Barr said.

He said the shooter deliberately damaged his iPhones during the attack. The FBI fixed the phones but FBI Deputy Director David Bowdich said so far, they can’t unlock them without Apple’s help.

“Even with a court order, to date, we cannot access the contents of the two phones,” Bowdich added.

Apple released the following statement:

“We were devastated to learn of the tragic terrorist attack on members of the US armed services at the Naval Air Station in Pensacola, Florida on December 6th. We have the greatest respect for law enforcement and routinely work with police across the country on their investigations. When law enforcement requests our assistance, our teams work around the clock to provide them with the information we have.

We reject the characterization that Apple has not provided substantive assistance in the Pensacola investigation. Our responses to their many requests since the attack have been timely, thorough and are ongoing.

Within hours of the FBI’s first request on December 6th, we produced a wide variety of information associated with the investigation. From December 7th through the 14th, we received six additional legal requests and in response provided information including iCloud backups, account information and transactional data for multiple accounts.

We responded to each request promptly, often within hours, sharing information with FBI offices in Jacksonville, Pensacola and New York. The queries resulted in many gigabytes of information that we turned over to investigators. In every instance, we responded with all of the information that we had.

The FBI only notified us on January 6th that they needed additional assistance — a month after the attack occurred. Only then did we learn about the existence of a second iPhone associated with the investigation and the FBI’s inability to access either iPhone. It was not until January 8th that we received a subpoena for information related to the second iPhone, which we responded to within hours. Early outreach is critical to accessing information and finding additional options.

We are continuing to work with the FBI, and our engineering teams recently had a call to provide additional technical assistance. Apple has great respect for the Bureau’s work, and we will work tirelessly to help them investigate this tragic attack on our nation.

We have always maintained 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. Today, law enforcement has access to more data than ever before in history, so Americans do not have to choose between weakening encryption and solving investigations. We feel strongly encryption is vital to protecting our country and our users’ data.”