The Twisted Ones

These were nice kids, model kids. They didn't wear leather jackets and roam the streets in "wolf packs"; they didn't steal and mug for dope. For kids, they were well mannered and quiet. They were attractive and nicely dressed. You'd have welcomed them as next-door neighbors.
Yet...
one raped
one murdered
one killed by fire
What got into them?
What dark thoughts tormented them when they were alone at night?