Whilst it is important to try to restrict access to weapons, we seem to be missing the obvious. Some people, especially teenagers, have a tendency to want to kill people. America has easy access to guns so they use guns. In London, it's knives. Also (recently) acid. In France it has been bombs and cars. Excuses range from religious fervour to sexuality. But the fact is - they will always find a way so the most important thing is to reach them before they do it and stop them. Incidentally I bet the biggest threat of all with teens is self harm