If young guys with ASD can't accept their social duty of being intimidated, harrassed, bullied, beaten, occasionally set fire to, etc for the amusement of their betters then there's plenty of suicide tutorials on Youtube - there's no need for them to go bothering normal folk!
sarcasm mode off
Not justifying it, but can definitely sympathise with the guy - been there, done that (to a lesser extent, but would quite happily have done worse if I'd had the opportunity). Snapping after years of bullying doesn't necessarily mean lashing out immediately. It can be more like a mental switch going off - the realisation that this really is all there is to look forward to in life (especially as this guy had left school, and it was still going on), that, actually, death or prison would be better, and there isn't actually anything stopping you from fighting back other than the rules of a society that's deemed you as it's whipping boy. There were several days between the first time I snapped and when I actually took action - doesn't mean that I wasn't mentally messed up during that period - to a frankly terrifying degree in retrospect, though I'd probably have passed any mental health assessments at the time. Treat someone as less than human for long enough, and there's a fair chance that's what they'll become.
TBH, I hope prison's the making of him. If he gets a room on his own he'll get hassled less than on the outside. For some folk, that's probably as good as life will get.
No sympathy for the girls - occupational hazard of being a bully and they'd have known the risks when they signed up. Besides (sarcasm mode re-engaged), surely by their rules, screaming 'die, die' is just banter, a beating is just spirited behaviour and a knife in the face is quite character-building? Or does that only apply if you're the bully?