Weren't these people charged as a 'joint endeavor'?
I always thought this is a bit dodgy. If someone you are with does something really bad, to what extend can you know it would happen, let alone prevent it?
Clearly if you watched them put a knife in their pocket earlier, but what if they just grab a weapon and strike straight away.
I think these people were in a different car, so could they really know their friends were planning on killing people by driving into them? Unless they could prove texts/phone calls/IM etc, then probably not