The former: someone had a gun and stopped the intruder and only a couple of people died.
The later: no one had a gun and the perp killed nine people.
Conclusion: banning guns is not the solution.
I saw a stat (on FR I think, but I cannot find a cited source) that said that mass shootings where an on-duty policeman was the first to shoot back averaged 12.4 dead per event... and those mass-shootings where someone else was the first to shoot back averaged 4.8 dead per event.
IF true and cited by a reliable source (and it certainly SEEMS true), then we need to be hammering this stat daily, in every public and media forum.