I need more help - my son is 14 and has been accused of things I don't believe his accuser. Please advise.

We recently heard that a child that we pressed charges against is going to press charges against my son for harrment. My son was attacked (this child came up from behind and clocked him, they were both suspended because my son tried to hit him back). It's a long story... but we pressed charges because this child has, for many years, threatened this and he scares me at what he might do again or to another child. The principal even lent that she thought something had to be done like that. I don't think he is stable. But I also think he makes things up to tell his parents for attention - like that people are picking on him. If my son ever said anything smart to him before, I am sure that has ended. We warned him over and over about contact with this child (since all of these events occurred), so I really don't believe he has "harred" him. I've never seen anything like that behavior before. Anyway, what can I do? This child has had anger management cles in the past... didn't work.