They still know right and wrong, regardless of whether the brain is fully developed, or not.
You don’t need a fully developed adult brain (and not all adults have fully developed brains btw) to understand the damn Golden Rule.
This is just assinine, and what I believe is that every shyster lawyer who uses this defense ought to be executed on the spot. And then his family fined $100,000 for wasting the courts’ time and providing crap legal counsel to his client.
I don't agree with you on that. I don't know that this jerk of a kid had even been taught right from wrong [I'd suspect not, but that would be racist]. Nonetheless, that does not or should not spare him from punishment.
That may be the only way he does learn.