I will say first, the parents of those murdered kids are going through hell on earth this Christmas without their children.
I can't imagine their grief.

There has been misinformation passed around on the weapons.
It was reported initially that the shooter was found with a Glock and a Sig.
A shotgun could be seen being taken out of a trunk by a cop in the vids.
I tend to think that the misinformation was just ignorant reporting (guessing).
Can't see a motive for the locals to fabricate an AR story in their "ban state".