While I agree this child should not be housed with adult prisoners in a regular prison, he definitely needs to be incarcerated.
I want to know more about his family background before saying he needs to be incarcerated. Where’s his mother? Meth addict? And how come none of the adults in this kid’s life seemed to have a clue that he was about to completely lose it? Just ignoring him, no matter how many red flggs he waved in front of them? Picture your sister eight months pregnant, and her eleven year old stepson tells you he wants to kill her. Would you not be taking some action, at least telling your sister, who in turn would presumably see to it that the kid didn’t have ready access to a loaded gun? There’s so much wrong with this picture that I can’t see holding an eleven old primarily responsible for the tragic outcome.