My information is the Secret Service snipers had Trump’s would be assassin in their sights before he fired the first shot.
However due to regulations they were not authorised to shoot him simply for climbing on the roof carrying a rifle.
They had to wait until he actually aimed at people – which then gave him the opportunity to fire the first shots.
All this is because Pennsylvania is an open carry of rifles state. The would-be assassin did not even need a Gun License to openly carry a rifle in that part of Pennsylvania.
Because the Secret Service officers were unable to conclude if the man was authorised to climb on the roof, because he was legally able to carry a rifle and because he had not yet aimed it at people, there were no grounds to kill him fast enough.