That's terrible, but it's a good opportunity to talk to your kids about how they (as normal kids) should rally around the victim and show him that he isn't isolated or alone in his struggle to be himself.
We can't always stop tragedy from happening, but we can help others to respond to it better than how it was handled when we were kids.
I think it is a natural herd reaction for kids to shun a kid who was beaten up so publicly -- it's scary in a bully environment to identify with weakness. So explaining to kids that it's important to fight against this herd mentality is important, I think.
Hopefully, the victim will be OK and will find peers to support his recovery. And hopefully the perp will be expelled, so he's no longer a threat (and interviewed to see if there's any trauma in *his* background that caused him to go rage-monster on the smaller kid).
Recovery is possible. Hang in there, brothers.