Why are we not satisfied with the prosecution of a mass shooter or terrorist?

Maybe it is due to the mysterious nature of these crimes that we crave additional action. They come out of nowhere and strike the innocent with violence that shocks and infuriates. These acts remind us that we are not in total control over the environment and that the barbarism of our past has not been lost to modernity. While violence in the world is going down we still find ourselves subject to nature's wrath but when it is by human hands we seek explanation and prevention.