My take on it is that it doesn't matter if he could have or should have stopped the younger people involved.  He should have just gotten in his car and drove away the minute he sensed it was wrong.  Assuming he actually is capable of  empathy and has a conscious to sense that the behavior is wrong rather than experiencing it as enjoyable.  
The school these individuals attended seems to be an issue for some because thay school is built so much on image and show especially with athletics.  But I wonder if he would have gotten the same sentence had he gone to a public school.  And not because he was a punahou graduate but embedded in that is that his parents would logically be more wealthy and better educated (assuming he wasn't there for sports and his parents actually paid tuition).  So he might have gotten better legal defense rather than a public defender or a selected psychologist  instead having one appointed.