*sigh*
Small caliber semi-auto handgun.
Probably from the stands to his right rear (viewers left). We'll have to wait for video from or of that location (and there will be at least some) to confirm what happened to the flurry of follow up rounds that were fired. It's possible those were fired as the shooter was being tackled by bystanders.
Not a professional.
*sigh**sigh*
It was a rifle.
From a rooftop just outside of the event.
Witness saw the shooter on the roof before he fired. Told police and Secret Service. They did not arrive at the scene in time to prevent the first shot.
The flurry of follow up shots was law enforcement killing the shooter.
The reason why it sounded like small caliber fire is the distance from the recording microphones.
@Render If this is the layout of the event, it was extremely negligent not to have security personnel on that rooftop - or the water tower which appears to be the highest point of the area.
There is an emerging trend to rely too much on drones for aerial surveillance. It is a good tool to supplement human surveillance - but it is insufficient by itself.