On Monday, U.S. Attorney General William Barr announced the expulsion of 21 Saudi military trainees from the country in connection with the fatal Pensacola Naval Air Station shooting that took place in December. 

Speaking at a news conference held at the Justice Department, Barr said the decision to expel the students came after an investigation of the Saudi shooter, Lt. Mohammed Alshamrani, determined that he was "motivated by jihadist ideology." The trainees were not found to have taken part in Alshamrani's attack - which the U.S. officially called "an act of terrorism" - but an FBI review uncovered troubling material on their computers and other personal digital devices.

"17 had social media containing some jihadi or anti-American content," Barr said. "However, there was no evidence of any affiliation or involvement with any terrorist activity or group. 15 individuals (including some of the 17 just mentioned) had had some kind of contact with child pornography," Barr stated. 

Of those expelled, 12 were trainees at the Pensacola Naval Air Station while the remaining nine were training in military facilities across the states. 

U.S. attorneys said the material did not warrant prosecution inside the country despite the fact that it featured child pornography and anti-American content. However, Barr confirmed the trainees would be dis-enrolled from service in the Saudi armed forces and are expected to face "harsh punishment" once they are back in the kingdom. 

According to Barr, Saudi officials committed to extraditing any of the trainees back to the U.S. if they are found to be implicated in the counterterrorism probe of the shooting — which is still ongoing. The official hailed Saudi Arabia's cooperation in the probes launched by the U.S. and said the kingdom had ordered all its military trainees in the country to fully cooperate with authorities investigating the mass shooting.

The Pentagon announced a ban on operational training for 852 Saudi students on U.S. bases in the wake of the Pensacola shooting. Classroom instruction for all those enrolled continued after "a DOD 'screening' of all Saudi military students training at U.S. bases found 'no information indicating an imminent threat'," according to ABC News

The Pensacola shooting left three dead

Source: Vox

The Dec. 6 attack left four dead, including the attacker, and injured eight others. The station where it went down "is the primary training base for all U.S. Navy, Marine Corps and Coast Guard officers pursuing designation as Naval Aviators and Naval Flight Officers."

Alshamrani was enrolled in the NAS Pensacola international students' training program when he opened fire on two floors of a classroom building near Radford Road on base. The shooting lasted around 15 minutes with law enforcement countering eight minutes after it began. The Saudi student was killed on the scene and was found to be in possession of 180 rounds of ammunition. 

The FBI took the lead in the investigations and found that Alshamrani had posted a message on social media on Sep. 11 last year, saying "the countdown has begun." 

Investigators also learned that he had visited the 9/11 Memorial in New York City in the weeks prior to the attack and had also posted anti-American messages online two hours before carrying out the shooting. 

FBI Deputy Director David Bowdich said the investigators interviewed "more than 500 people" and they are still coming across leads. He added that the agency could confirm that Alshamrani "had studied Al Qaeda's U.S.-born cleric Anwar al-Awlaki." 

Al-Awlaki was killed in a 2011 U.S. drone strike and is believed to have inspired a large number of radicals. 

During Monday's press conference, both Barr and Bowdich said it was difficult to access the attacker's two iPhones even though they were repaired by FBI technicians. They blasted Apple, saying the company did not cooperate with investigators' requests to help access the devices that Alshamrani sought to destroy during his attack.