 Federal law enforcement sources tell us it was local law enforcement who had responsibility for securing the rooftop. It was rally-goers who first spotted the gunmen crawling on top of the building. Sources tell us one officer climbed to the top of the roof, saw Crooks armed with a rifle, and retreated. Soon after that, Crooks began to fire, according to the source. And we know moments later, a Secret Service countersniper shot and killed the gunmen.