Shein
I think theres a huge difference between an 11 year old boy and a 15 year old boy.
The Torah considers a 13 year old a bar das. The 15 year old should have asked for help instead of destroying a 6 year old girls life. If he had taken a gun and shot her through the eyes you would have no problem viewing him as a monster. Well what he did is beastly and monstrous.
I have no idea if he was molested as a child, but even if he was he should have gone for help I have no pity left for someone who ruins an innocent childs life the way this boy did. If he was 11 maybe I would have pity but I dont pity a 15 year old boy who does such a thing.