I think you might be off in law enforcement call.

I think its more specific than 'law enforcement'.
But at the same time, it is more broad than 'law enforcement'.

Even in a 'martial law' type situation, you still have violence.
So, what stops the violence?

Saying the gun is the problem, that's like saying you don't like an article, so the pen is the problem.

Saying the shooter having access to the gun is the problem, well thats like saying a drunk driver killing someone in a crash, it was the him/her having access to the car.

Well, that just as stupid. It was the driver. The driver and his/her choices in life.

Now, I DO think the ones that did not respond are at fault for not stopping the situation faster.