
Quoting
llworking
You could make a police report about the threats, that might possibly cause the school to take things more seriously. You could also get a lawyer involved to talk to the school to make them understand how seriously you take the situation. You can also escalate things being the school administration to the superintendent's office.
The school is in a tough position because he is also being bullied and because his rights matter as well. However the safety of the students should be the primary focus. Basically what you need to do is make as much "noise" as possible about the situation without going on a witch hunt.