 Well, we'd already been hearing these reports about people spotting the gunman on the roof before he started shooting. Now there's a video circulating on social media. This is a video that NPR has not independently verified, but it appears to show that happening. So the big question here is how was a man with a rifle allowed to get up there? This building is about 400 feet from the stage. It's outside the perimeter where people were being checked for weapons, but that roof should still have been secured. At least that's what retired Secret Service agent Kerry O'Grady told me.