 The morning of the event, congressional sources telling ABC News, the shooter came to the fairgrounds for an hour and later returned at 5 p.m., approximately one hour before he opened fire. Law enforcement sources tell us he was spotted walking near the magnetometers, did something suspicious, and was approached by authorities. He backed up and faded into the crowd. Those lawmakers also say the Secret Service knew that Crooks was on the roof a full 20 minutes before he fired his first shot.