This is very tragic. I hope your son gets better soon and suffers no lasting effects. It is good to hear he was not seriously injured.
There is no excuse for what this driver has done and he deserves the highest punishment allowed by law. But you have to remember he was drunk and most likely pissed off . When you have a group of cyclists getting together for the sole purpose of pissing off drivers, there is bound to me some moron out there that want to do someone harm. I certainly hope other CM riders learn from this tragic event and consider the consequences before they participate in their next CM ride.