It also happened at that law school shooting (?) where two guys got their guns and stopped the shooter. Too lazy to search for it but that aspect was completely ignored by the mass media.
In a Pennsylvania case, a home owner with a shotgun apprehended the shooter. I think Lott says it has happened about 30% of the time that a citizen with a firearm helped save the day.
In the Texas Tower shooting, once the citizens started shooting at Whitman, there were no more killings.