Unfortunately it does not take long to do brain damage.
Children today watch ridiculous violence presented in games and media in unrelistic ways. They see things that would kill people, and the guy just gets up and takes several more of the same. They may not have actually realized that their action were life threatening.
Of course that does not excuse it. The minimum charge should be manslaughter.
School is 53 percent Black. Sadly more than 20 percent is the tipping point. Higher than this, schools become dangerous, chaotic. Not PC to mention this, but it’s a fact of urban life.