The FBI has reportedly asked Apple for help in unlocking two iPhones that investigators believe were owned by the man suspected of carrying out a deadly shooting last month at Naval Air Station Pensacola, Florida. NBC News reports the FBI sent a letter to Apple’s general counsel late Monday stating that it can’t get access to what’s in the phones—believed to have belonged to Mohammed Saeed Alshamrani—because they are password-protected. “Investigators are actively engaging in efforts to ‘guess’ the relevant passcodes but so far have been unsuccessful,” said the letter. Authorities are also struggling to gain access to the phone because Alshamrani reportedly fired a round into the device during his attack. Apple said in a statement: “When the FBI requested information from us relating to this case a month ago, we gave them all of the data in our possession and we will continue to support them with the data we have available.” Alshamrani, a member of the Saudi air force who was in flight training, is suspected of killing three people in the shooting before he was shot dead.