US Attorney General William P. Barr declared the shooting at Naval Air Station Pensacola in December an “act of terrorism” on Monday.

On Dec. 6, Mohammed Saeed Alshamrani, a Saudi military officer who was in the US for training, killed three US Navy sailors at the Florida naval base with a handgun.

An investigation into the shooting revealed that the shooter was motivated by jihadist ideology, Barr said.

The US found that 21 other Saudi nationals in the US for training were in possession of concerning materials, such as jihadist or anti-American content and even child pornography. Saudi Arabia is pulling them out of the US and will be reviewing their cases in accordance with local military justice codes and criminal law.

Visit Business Insider’s homepage for more stories.

The US attorney general, joined by FBI officials, declared the deadly shooting at a Florida naval base last month an “act of terrorism” on Monday, revealing that 21 Saudi nationals training in the US are being sent home.

On Dec. 6, 21-year-old Mohammed Saeed Alshamrani, a Saudi military officer who was in the US for training as part of a three-year program, used a 9mm to open fire on US Navy personnel at Naval Air Station Pensacola in Florida. He killed three sailors and injured a handful of others before he was killed by local law enforcement officials in an attack that shocked the nation.

“This was an act of terrorism,” Attorney General William P. Barr said Monday in a statement released by the Department of Justice.

He explained that the shooter appeared to be motivated by “jihadist ideology,” adding that he regularly posted anti-American, anti-Israeli, and jihadi messages on social media. He did so just before he commenced his attack, during which he “proceeded to walk around shooting down his unarmed victims in cold blood,” the AG said.

Alshamrani posted on social media on Sept. 11 last year that “the countdown has begun. He is said to have visited the 9/11 memorial in New York City over the Thanksgiving weekend.

It is unclear exactly how his social media activity was missed during the vetting process, but previous media reports revealed that Alshamrani had a secret Twitter account that did not include his full name, a photo, or any biographical information, making it harder to find. An analysis of this account, discovered after the shooting, showed that the shooter may have embraced a radical ideology years before the attack.

Lees ook op Business Insider Kabinet: Nederland zit in tweede coronagolf – horeca in zes risicogebieden vanaf 1 uur ’s nachts dicht

Following the shooting, the Department of Defense ordered a pause on operational training for all Saudi military personnel training in the US, a decision that affected roughly 850 students.

Barr explained that while there is no evidence that other members of the Saudi military had prior-knowledge of or assisted Alshamrani before or during the attack, the investigation did reveal that 21 members of the Saudi military in the US for training were in possession of concerning material.

“Seventeen had social media containing some jihadi or anti-American content,” Barr said in the DoJ statement. “However, there was no evidence of any affiliation or involvement with any terrorist activity or group.” He added that “15 individuals (including some of the 17 just mentioned) had had some kind of contact with child pornography.”

The trainees, he explained, will not faces charges or federal prosecution.

Saudi Arabia has decided that the material evidence constitutes conduct unbecoming an officer of the Saudi Royal Air Force and Royal Navy. “The 21 cadets have been dis-enrolled from their training curriculum in the U.S. military and will be returning to Saudi Arabia,’ Barr explained.

He added that Saudi Arabia has promised to review each of the cases in accordance with the country’s military justice codes and criminal law.

The Pentagon said in a statement Thursday that during the course of the shooting investigation, investigators identified 21 members of the Saudi military in the US for training that were “engaged in activity that raised serious concerns.”

“Upon notification of these circumstances, the Department of Defense worked with the Kingdom of Saudi Arabia to withdraw the students from training and in consultation with the Department of Justice, the DOD worked with the Saudi Embassy in the United States to return these students to Saudi Arabia.”