You missed my point. There is not even a trial where the McClean family can get a bit of closure. If you don't think having a psychopath stab, behead, and mutilate a young son in public, not even mentioning the cannibalism, is worse from the family's point of view than your average run of the mill shooting, you are writing in a vacuum. McClean's family will be having nightmares over this for as long as they live.
Why would a trial give them closure? They'd get to hear all the details over and over again, not to mention the ensuing media coverage. I don't see how that would be helpful. They would learn nothing new, but have to continue reliving it day after day in the public eye. They know what happened to their son. They know who did it. They know what our law deems as appropriate punishment for the mentally ill. That's all a trial could tell them.
I think it's appropriate btw. Someone who can't distinguish reality can't be criminally responsible for their actions.