Well, for one, I am never a fan of people ganging up on one person. If you're going to be "man enough" to fight, then fight one on one. Don't grab your "crew" and/or your "boyz". Just honorably tell the person to step outside. And unless your life is in danger, no biting, no kicking where the sun doesn't shine, and don't kill the guy. I have no idea how society in general degrades into animals when fights break out. But anyway, that's why I have no sympathy for the three people who decide that humming is an act that deserves a beating. I understand that it might have been annoying, but unless it was against the rules there's really nothing you can do about besides asking politely for him to stop.
As for the knife guy. He might be able to argue that he was acting in self-defense. It is tough to determine if three guys beating you up is out for your life. And who knows what happened when he pulled out his knife? Did he tell them to stop? Did he say "back off or I will protect myself"? Beats me. For now, it'll stand that he went beyond what was necessary to protect himself. I wasn't there, so I can't really say. But he must have went for some vital points for one guy to die at the scene and another to die later that night.
In the end, all this could've been avoided if the three people requested the man to stop humming. And if he didn't, then they should've sucked it up or move to another car. There's no way to justify beating up the guy for humming. That's just ridiculous.
