"Given the recent attacks at two military installations, the Commander, U.S. Northern Command has directed all DoD [Defense Department] installations, facilities and units within the U.S. Northern Command area of responsibility to immediately assess force protection measures and implement increased random security measures appropriate for their facilities," Lt. Cmdr. Michael Hatfield told Fox News.

While officials have not publicly disclosed how many missing servicemen are out there, U.S. Northern Command (Northcom) has called for increased random security checks at all sites as authorities investigating the attack are still working to determine whether the shooting was an act of terrorism. -Fox News

Meanwhile, the FBI is searching for missing Saudi nationals linked to the shooting. The agency's Jacksonville office confirmed that the shooter was Mohammed Alshamrani, 21, a 2nd Lt. in the Royal Saudi Air Force and a student naval flight officer of Naval Aviation Schools Command when he killed three people and injured 12 after opening fire.