Why would you do it? Why would you enter a building full of beautiful young people having fun, doing you no harm — doing nobody any harm — and kill them?

Why would you do it? Why would you drive along a road mowing down tourists or shoppers, blow up a shopping centre, murder athletes, stab an off-duty solider, kill a cartoonist, ram a plane into a building, destroy a nightclub and the people in it? Why?

It’s hard to fathom what goes through the mind of such killers, especially when they die themselves. There are studies on their religious motivation, studies on their socio-economic background, studies that say they are already suicidal, studies that say equally vehemently that they aren’t.

But one part of