Trump shot?

[ArMaP]

They probably saw him leave the group in the direction of the building, and then saw him get up on the building.  If you watch the video, you will see it's only about 50-60 FEET from the building, so not far away at all.

I watched the video, but that's the problem with videos or photos without enough context, we can't judge the distance based on a video from an unknown camera, as we can't know if there was any kind of zoom in place.

Where was the camera (and the people around it)? In the event grounds? On the private property where the shooter climbed to the roof of that building?

After writing the above I went looking for more information and found a video that appears to show a wider view, so we can see that people were close to that company's buildings, although we still can't know the distance, but it appears to be real close to the building, so dismiss what I say above, at least in part.

Edit - Someone over on ATS posted a picture of the security perimeter around the event.  In the aerial picture there was a pie shaped piece cut out of the circular secured perimeter, and this is where the building was that the shooter was on top of.

If you could post that picture it would be great.