PENSACOLA, Fla. — The attack killed three American servicemen and wounded eight others.

The shooter was a 21-year-old Saudi Air Force second lieutenant going through flight training at Naval Air Station Pensacola. And, during a Monday news conference,  Attorney General William Barr said he was a terrorist.

As investigators began digging into Mohammed Alshamrani's background and trying to uncover his motive for the Dec. 6 attack, flight training for another 175 Saudi students was suspended.

Now, at the request of the Saudi government, 21 will be expelled from the United States, according to Barr. The Justice Department says they all had "derogotory materials."

According to investigators, 17 had jihadi or other anti-American content on their social media accounts, according to investigators. Fifteen – including some of the 17 above – had "some kind of contact with child pornography," according to the DOJ.

One had a "significant number of those images," Barr said.

The attorney general said U.S. attorneys reviewed the information and decided there was not enough evidence for federal prosecutions, but the Kingdom of Saudi Arabia determined the 21 cadets "demonstrated conduct unbecoming an officer."

They will be sent home on Monday.

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Attorney General William Barr
AP

The Washington Post reports the Saudi government has cooperated with the FBI investigation

Barr also reiterated the government's request for Apple to assist in the investigation. He said the shooter had two iPhones, and investigators need to find out who he was talking to.

Apple has refused to help crack the passwords, citing customer privacy concerns.

RELATED: FBI to Apple: Help us unlock iPhones used by suspected Naval Air Station shooter

Secretary of Defense Mark Esper told CBS Face the Nation on Sunday that the government is taking steps to make sure nothing like this happens again.

“I've signed out directives that address enhanced screening of all of our foreign students that address credentialing going forward, weapons policies, etc.. So we're doing everything we can,” Esper said.

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U.S. Secretary of Defense Mark Esper
AP

That will likely provide little comfort to the families of the young men who were killed.

Twenty-three-year-old Ensign Joshua Kaleb Watson of Coffee, Ala., 21-year-old Airman Apprentice Cameron Scott Walters of Richmond Hill, Ga. and 19-year-old Airman Mohammed Sameh Haitham of St. Petersburg, Fla, were killed in last month's attack.

The U.S. Navy posthumously awarded them Wings of Gold.

The Florida Senate will honor them, the survivors and the first responders on Tuesday in Tallahassee.

3 sailors in NAS Pensacola Shooting
From left to right: Airman Mohammed Sameh Haitham, Ensign Joshua Kaleb Watson, and Airman Apprentice Cameron Scott Walters
Provided Photos

RELATED: Florida Senate will honor first responders, survivors and those killed at NAS Pensacola

RELATED: Posthumous honor: U.S. Navy promotes hero sailors who saved lives during Pensacola shooting

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