There is the problem in a nutshell. Probably nothing is going to happen basically. Except the endless media coverage perhaps giving some other maladjusted individual stimulation to consider some simular avenue of approach. There are enough mental basket cases out there to go around.

His shooting his mother and the students could have been simple revenge in his mind for his mothers failings as a mother in his opinion for example. Or perhaps she did exibit enough backbone reciently not to put up with his crap anymore and he responded in a fashion.

Terrible I know but things like this are possible as a small percentage of the population evolve with no evidence of having any consience at all. Whatever it is sick but to call it a mental illness may be so but conclusivly so perhaps not. To blame others for your own failings is also another possible common venue. When you combine this with any of many other factors things like this can result although this example is extreme. What I wonder and probably will never be known. Was there any indication he was very far from the norm in general behaviours and getting progressivly worse?

Considering any form of gun control once they have been dispersed through society tends to be pointless. We had a gun registry system for a few years up here in Canada. The result? Many guns went into hiding and were not registered. Or some owners only registerd a few of theirs. The program cost more than billion dollars or perhaps two billion before it was dropped. It achieved almost nothing.