It's been happening for a long time. It's simply easier these days for somebody who goes completely off the lunatic fringe to acquire firearms and go on a rampage through densely-packed community hubs. Gun control is the problem. Here in Australia, gun control was implemented after a wealthy 20-something guy named Martin Bryant went on a killing spree in Port Arthur and executed 35 people and injured over 50 more in '96. He went so far as to chase two little girls into the woods after killing their parents and executed them both as they cried and hugged each other. People were pretty sickened by guns after that. Since then, gun deaths in Australia are virtually non-existent, and although they were a hobby of mine as an air force cadet, I recognise that statistics don't lie. Every country with strict gun control is among the safest in the first-world with the US being the most dangerous industrialised country. They say people would just use knives and other weapons if guns weren't available, but I bet the guy at the cinema couldn't have killed and injured all of those people with a knife.
Guns are only a tool. They are neither good nor bad. The decision to take a life lies in the mind of the person, not the gun. If a person is inclined to commit mass murder they choose the gun as the easiest, most efficient tool to accomplish it. They could just as well choose an axe or a chainsaw but these would not be as easy or quick to use and more innocent victims would have time to escape.
It's apparently much easier to get guns than it is to get a loan in this country. Plus it's so easy for a person to get a new "toy", get high, go nuts and kill people and then claim temporary insanity. Our rules and punishments are too weak for these people, forget jail and sitting on death row, turn them loose to the families of the victims, or even society in general.