He most certainly is a murderer, no argument there. For whatever reason you’re giving the school a free pass as there were several things that should, and legally could, have occurred. First and foremost, keep the kid in the office where any potential harm is largely mitigated to adults. Second, search the kid, his belongings and his locker, if he has one. Turns out they could have expelled him had they done that. Third, assign the kid to online classes. If the parents refuse to take him at that point, call CPS as he’s been abandoned by his custodians and is a dependent child. Fourth, summon the SRO and have him transport the kid to the local hospital for a 1036 psychiatric hold.
To say that the school had no options is just wrong. If you want to open the can of negligence beyond the heinous shit this kid did, you have to open it all the way. That’s my point.
ETA: and under no circumstances should the kid have been sent back to class.