I'm just looking for ANYONE to come up with ANY remotely plausible law (including a AWB) that would have prevented this guy from stealing his mother's guns after murdering her, thereby preventing this tragedy.
NAME ME ONE.
I actually pay attention to the Brady Center and their proposals. Not a single one of them would have in anyway interfered with this atrocity.
The only way you could hope to stop this kind of thing is with a ban on ALL privately owned arms. That would cost, assuming that we didn't ALSO throw out the 5th amendment, about a trillion dollars.
That's just in buybacks assuming a 100% compliance rate.
Over the weekend several people suggested an Australian style full semi auto / handgun ban and buy back would curb future killing sprees with guns. If you make guns impossible to obtain legally, then over time it becomes extremely difficult for crazy people to get access to them, even on the black market, because they are expensive (a black market AR in Australia is over $10k) and a mental case is unlikely to have connections with organized crime.
I'm guessing in the US that it would probably take decades to achieve what Australia did in a few years, but it could be done if you are willing to throw the Constitution out the window, and live in a police state. Since the War on Some Drugs and the Patriot Act already established most of the necessary mechanisms for a police state, and 9/11 demonstrated that most Americans don't care about the Constitution (specifically the 4th), I think it's possible, although unlikely.
Of course, that won't stop future crazy people killing with knives, explosives, bull dozers etc, but nobody wants to hear that right now.