So what I've gathered thus far is that basically what it all boils down to is that over the past 100 years the major changes when it comes to gun laws is an increase in restrictions. Concerning the criminally insane or just mentally ill people with the potential to carry out violent acts, well there are just more of them out there on the streets (since we no longer as a society find it just to lock them away like we use to).
I don't see why people are even discussing tighter gun control legislation since it either plays no role in the increase in this type of gun violence or it possibly makes things worse given the overall trends in our society.
I think what we have to look at is our treatment of people who are mentally ill specifically those with a potential of doing some sort of physical harm to others. We need better treatment and as much as people probably are not going to want to hear it we need to be stricter when it comes to their personal liberties in order to protect the rest of society. Either way, like many have already stated I think this is exactly where we need to be looking in order to come up with some sort of feasible action plan.
*my response is based on an overview of what I've been hearing and is subject to change
It would help to do a case study on each state and town where such violence has taken place, study the people, study the laws and see if there are any significant trends.