 ABC News Chief Justice Correspondent Pierre Thomas. There was a clearing of the building. They thought that it was looked at earlier, that there was no one on top of the roof. But the key thing is somehow, at some point, that suspect was able to get on top of the roof and then start inching toward being able to make this shot. Pierre Thomas, Don Mahalik, former Secret Service agent and ABC News law enforcement contributor. Finding out the motive is always key, as the Secret Service has taught us,