Not that it would be excusable if done to a stranger, but even if getting back at your girlfriend by killing her son and leaving his severed head where she'd see it could somehow be justified, you'd think some vestigial shred of human decency would have stopped the guy from murdering his OWN loving son, propping up the head by the roadside and stuffing the body in a trashbag like old newspapers. Anyone who'd do something like THAT to his own child for such a petty reason should be permantly removed from society, because they're clearly capable of doing anything to anyone for any reason.