It sounds to me that the biggest problem here was that this kid's mental illness was never adequately addressed. That's been an issue for many years in this country, when decisions were made to release the mentally ill from hospitals to lower costs, and to allow the mentally ill to be treated by drugs and talk therapy rather than institutionalizing those who in the past would have been considered dangerous to themselves and others.
Unfortunately, many of today's society would rather take away the guns than hospitalize the seriously mentally ill.
The biggest problem here is that schools are defenseless.
This is going to happen again.
Not only are we inviting it, we are enabling it.