*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.
@Minholkin @Render yeah Render is right... this will play into the whole Trump as Jesus mindset. Fucking terrible.