President Donald Trump has urged Apple to help unlock iPhones used by an attacker during a fatal shooting at a U.S. naval base last month. "We are helping Apple all of the time on TRADE and so many other issues, and yet they refuse to unlock phones used by killers, drug dealers and other violent criminal elements," Trump tweeted Tuesday. "They will have to step up to the plate and help our great Country." At a news conference in Washington the day before, Attorney General William Barr had said the Justice Department asked Apple for their help in unlocking the shooter's iPhones, but the tech giant has not given it any substantive assistance. Barr called on Apple and other technology companies "to help us find a solution so that we can better protect the lives of Americans and prevent future attacks." The shooter is said to have possessed two Apple iPhones. Three U.S. sailors were shot to death by a Saudi trainee at the Pensacola Naval Air Station in Florida on December 6. Eight other Americans were severely wounded in the attack. The assailant, 2nd Lt. Mohammed Saeed Alshamrani of the Royal Saudi Air Force, was killed. The FBI had received court authorization based on probable cause to search both phones in an effort to trace all leads and figure out with whom the shooter was communicating. During the gunfight with first responders, the shooter disengaged long enough to place one of the phones on the floor and shoot a single round into the device. It also appears the other phone was damaged. Experts at the FBI crime lab were able to fix both damaged phones to revive its operation. However, both phones are engineered to make it virtually impossible to unlock them without the password. Barr said it is very important to know with whom and about what the shooter was communicating before he died. However, Apple rejected the claim that it did not help officials in their investigation.