Smo, you say you can't understand why they did it - the simple answer is, no-one can.
It's human nature to look for rational reasons for irrational behaviour, it comforts us to understand.
But the truth is, there is no answer.
I am sure the boys were asked numerous times why they acted as they did, and I am sure they said they didn't know, and as unsatisfactory as that answer is, it's the truth, they don't have a reason because there is no reason, as Bob Geldof memorably said.