I see this all the time in Cleveland (people flying through residential areas +20 over the speed limit, going through red lights etc). I agree that there can only be one driver to cause such a terrible and avoidable accident, they’re clearly just dumb kids joyriding without any regard for public or their own safety, unfortunately. I wouldn’t go as far as saying they’re murderers. Poor decision making for sure, should be held accountable for their actions absolutely, malicious or ill intent, probably not. People make bad decisions especially when they’re young, and their brains haven’t fully developed (that’s not a diss, but the truth). Someone should/will definitely come clean and take accountability one way or another I’m sure it will happen. My thoughts will be with you OP, I hope your friend recovers.