I don’t think he can check out. The story is kind of screwed up. Who provided the alcohol and Valium? I’ve met people who killed people drunk diving. 20 years might had been merciful.
I know a guy who killed someone in a car accident. He has no memory of the incident, and was never in legal trouble over it. However, he continues to beat himself up about it, and is terrified of driving again.
Sometimes, prison helps the perpetrator as well as serving society. The perpetrator who has a conscience and spends time in prison then feels he has been properly punished and is able to get on with his life.
This kid needs to be punished, regardless of whether he feels he did anything wrong. Otherwise, he is likely to repeat the behavior. Maybe when he is an adult, the law won’t be so lenient.