I'm not about to blame a 12 year old for their actions. Life as a bullied kid can really, really suck. Depression and suicide are common effects of bullying, and as a kid you just don't have the knowledge of how to deal with it.
If you bully / mentally abuse somebody to the point that they commit suicide, my opinion is that you are just as culpable as if you had murdered them yourself. By that standard, I don't see much difference if the victim decides to lash out and take their bully with them. Especially if you're a kid with no long term perspective. If you're in that situation as a kid, you're a victim and the system has failed you.
Maybe if the 12 year old bully had been held responsible for his behaviour then none of this would have happened. But you can blame a 12 year old for their actions, right?
I know you're being sarcastic, but I actually do agree. It was on the adults to make the situation better, not expect kids to be empathetic enough to not bully others
If kids can't be expected to not bully others then what can the adults do? If a child bears no responsibility for their behaviour then how do you get them to change? I really don't understand.
Educate the bully, punish the bully, remove opportunities for the bullying, whatever your preferred method. The onus is on the adults to prevent or put a stop to the bullying. The fact that things escalated as much as they did means that none of them stepped in, and that failure is on them.