Get the local TV station to tape a pre-interview with you and your son

the LAST thing you, the school or the other child's parents want is the media. They will NOT solve the problem; just make life difficult for all involved. Especially your son.
What actions is the school taking to moderate this child's behaviour? It really doesn't sound like there is much being done. Maybe, and I hate to say it, there are drugs the boy could take until he grows out of this rage cycle.
Have you talked with or know what the parents are doing with this child? If they're not doing anything, they're negligent.

I hope you've talked to your son (it sounds like you have) about this boy. You should be really proud of him that he understands that DP should be avoided where possible AND that he shouldn't retaliate if anything does. He's a brave lad.

Expulsion may be the answer, but it would be best, perhaps, if the family concerned moved DP to a school that could better cater for his needs. It sounds like he has a few. Vilifying him relentlessly wont help him.