Saw a show on cable about the 15 worst mass murders, or something to that effect.
On one, the Texas tower, those of a certain age will recall. In the course of the segment they said "a well armed populace helped keep the sniper pinned down, thereby possibly reducing the number of casualties." I haven't checked on that, but it sounds about right.
If correct, three cheers for carriers!
Wasn't the only one mentioning help from bystanders.