Why should the US in particular be prone to such attacks? They are far more frequent in America than elsewhere in the world (though appalling atrocities have occurred in Russia, Israel and a number of European countries).

One factor, for many, defines America is access to guns. If kids could not bring guns to school, we wouldn't have Columbine or Virginia Tech (where 32 people were slaughtered by 23-year-old student Cho Seung-hui in 2007). Or, now, Oakland, Professor Ochberg might have added.

"The reason we have an American school shooting problem that exceeds other nations has to do with access to loaded weapons by kids who should not have that access. Any serious attempt to prevent school shooting will have to attack the problem," he said.

It is not a view likely to win wide support, especially in states with a powerful gun heritage. Some commentators have argued that the problem has less to do with guns and more to do with civil liberties.