Tighter enforcement of gun control laws might be helpful in some types of crime, but not in crimes like this.

The guy's weapons were all legal, so the evidence suggests the opposite. It's quite possible he bought the weapons when still sane (or at least, not crazy enough to be refused them) and then flipped. He seems to have been a compulsively law-abiding hyper-conformist religiously obsessed prig.

The sort of case that comes to mind is that of James Clerk of Eldin, one of the leading judges in Scotland in the early 19th century. His family had hereditary Alzheimer's. After a distinguished legal career, somebody found him firing a pistol out of his window into pitch darkness trying to hit invisible demonically possessed cats. (Fortunately nobody got hurt).

That could happen to anybody. Here's Kendall (who owns much more and better weaponry than Clerk of Eldin did) in another thread, talking the "home invasion" scenario:

However, if you catch him "Red handed", that's a different story; then, he may pose a deadly threat to you and you have a right to defend yourself, or your wife's honor.

Is Kendall uniquely immune to getting Alzheimer's or a stroke affecting cognitive function, and imagining such a threat?