they weren't killed at one time, it was spaced apart over a few minutes. If a gun some how killed 17 people at exactly the same time, we'd be screaming about quantum mechanics right now, and not a rifle.
But people understand quantum mechanics around here about as much as they understand guns, healthcare, religion, abortion, war, lgbt, groupthink mob mentality, and torture.
So by all means, lets keep diverting the issue away from the obvious, and blame guns more!