"Mateen’s social media accounts were taken down before they could be widely viewed by the public, but Johnson’s committee investigators have uncovered some or all of them. The senator has also written a letter to Facebook executives expressing concern about Mateen’s postings and asking for more information on his activities. "“It is my understanding that Omar Mateen used Facebook before and during the attack to search for and post terrorism-related content,” read Johnson’s letter. “According to information obtained by my staff, five Facebook accounts were apparently associated with Omar Mateen.”"