After the Newton, Connecticut shootings, people will be asking, "Why did he do it?" To many, the answer will be self-evident: "Because he was mentally disturbed." No mentally sound person would do such a thing.
But the question is the wrong one. What we should be asking is, Why do people who are similarly mentally disturbed but living in other countries not do it? The answers in this case are not so self-evident, but some spring to mind.
They are not mutually exclusive. If we are to take seriously our responsibility to protect children and other possible victims we should consider each of them, because in New Zealand we are not necessarily permanently exempt from such a disaster.
One possible answer is that there is a particular kind of mental disturbance that is more common or less well treated in the US which leads to this lethal behaviour. This seems unlikely.
Another answer is, because they don't have ready access to multiple-shot deadly weapons - which, if we are to learn from the tragedy, takes us down the path of not ever in New Zealand making guns as readily accessible to even the most irresponsible of people as they are in the US.