it is scientifically proven that the brain does not fully develop until about age 25-27.
Yes, he knows right from wrong but the segments of the brain that can fully comprehend the consequences from actions are not developed. He would understand that hitting is wrong...but would not have been able to compute that "possibly, the person will die". I see it more as unintentional manslaughter. Yes, he meant to punch them (and that was wrong) but, he would not have thought he could kill someone.
I strongly believe that there should be a separate section of prisons for young offenders so that they are kept separate and safe from the other inmates, safe from rape and violence that happens EVERY day and night in prison.
Yes, i believe that the parents should share the responsibility for his actions. You don't get to wipe your hands of them just because they have a birthday. For eg when my ex cheated on me, my inlaws felt responsible (even though he was 30) because they felt it must have been the way he was raised. It doesn't matter that he is grown, he was a sum of his upbringing and experience.
Sometimes, it is about the dominant discourse of the area they are raised (someone used the example of the treatment of the cameraman) and this can be hard to combat as a parent.
Sometimes, regardless of upbringing, kids can make really stupid choices and mess up...like this kid has. BUT, putting him in prison with violent offenders that will destroy him...is not the answer.