I don't know about you, but I use gun cases, of various sorts, to transport my long arms.
Must have been a fairly short shotgun. Maybe even one modified into an untaxed NFA weapon? If so, one more gun law that never saved anyone.
Could have even been a break down single shot I hope not though.That would mean at least 5 chances to disarm him. Six people shot and if I read right more shot at. Now even with the plug out most hold what? 5 shells? Meaning he had time to do a reload too most likely. In close quarters the shot would not scatter that much.
I just read another update. One woman was in a room off from the others saying she heard several shots. It sounds like the perp had a sawed off pump to me. {Guessing} That would explain better few shots being fired and 6 hits with a kill.
Folding stock, pistol grip, a hacksaw or all three .......
Bad deal regardless.
Stay safe !