Give his other letters that are coming out, I'd definitely say that he had some serious unchecked mental issues, given his ridiculously high amount of paranoia.
Since we can't "fix" the lack of gun control in this country because of the amount that already exist freely, and the amount of lobbying power the NRA has, the next best option is to focus on the underlying mental issues and lack of mental health in the country if the end goal is "less people dying." This is similar to working on the underlying social issues that cause crime in the first place to solve widespread crime issues. But again, that's if someone's focus is to make things better for everyone.