There is no way of predicting when someone will 'crack' and go on a shooting 'spree', but if there are no guns around then the guy has to think of another way to release his anger and frustration. He might well kill himself but he won't take everyone else out with him.
It's funny you should mention that, we had a guy over here in the U.S. who killed 168 people and injured nearly 800 people. And he didn't even use a gun, he used a truck bomb. Point is, the nutters will find a way. Here's a link in case some of you might not know who I talking about:
And that's how I know trying to eliminate mass killing with gun control will not work in U.S. As I said, the nutters will find a way. Vehicles and bombs, worse killing method compared to a gun.