According to a CNN report, Thomas Crooks purchased a five-foot ladder on his way to the rally and was able to somehow carry this ladder along with his rifle to a building with a direct line of sight to Trump's podium, a building that was occupied by heavily armed police.

Tonight, ABC News has learned that heavily armed local police were stationed inside that building

and missed Thomas Crooks climbing up the outside of the building to the roof.

With rifle in hand, Crooks used this ladder to climb the building and was spotted on the rooftop 30 minutes before he opened fire.

He was photographed by police and reported 25 minutes before the shooting.

He was even confronted while on the roof before the shooting.

The local police officer climbed up the roof and confronted Brooks moments before the shooting.

The officer grabbed hold of the edge of the building, pulled himself up to be able to look.

And according to what he's told me, shooter turned, rifle was pointed at the officer.

The officer defensive move, got a duck, fell, lost his grip on the building.

Bystanders began pointing out crooks to police a full two minutes before he opened fire.

Look, they're all pointing.

The Atlantic, maybe the Pacific.

Yeah, someone's on top of the roof. Look.

There he is right there.

Right there, see him? He's laying down.

See him?

Yeah, he's laying down.

The defensive sniper detail was looking directly at him a full 40 seconds before he opened fire and allowed him to fire a few shots before taking him out.

The first shot fired grazed Trump's right ear as he turned his head towards the shooter. Had he not

turned his head, he would have been murdered on live television. We call that DRT, which means

dead right there. And so what that means is all sympathetic, parasympathetic nerve response

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