So do I have this right?
An off-duty Border Patrol agent ended this by effectively getting into the school via his credentials... and used a buddy's shotgun?
As for parents trying to get into the school, I don't blame them. I'm also not surprised police stopped them - especially anyone armed. They decided it necessary to resort to making entry themselves - armed or not - because the police weren't, yes. But, as an incident commander, I would not allow any civilian (armed with good intention or not) inside of that school. If that civilian accidentally shot an innocent... yikes.
I would, though, be sending in officers after this guy even if it was a barricaded suspect situation. It's a school. There are children in there... I'm sending in the officers, end of discussion. Especially when I had no video evidence that the situation was indeed a barricaded suspect.
Look... people are often saying... "police should not be getting military training!" To which I reply, if they all had it properly in this situation, they (meaning the regular officers not a SWAT team) would be able to quietly chase the gunfire/shooter, identify the shooter's location, and surprise him at his doorstep to take him out -- all in a coordinated fashion and with minimal risk. Never mind placing a sniper such that they could shoot into the classroom the shooter was in. Risky to shoot through a plate glass window, but if he ever got close to the window...