I am sorry but.....
The friend (or ex friend) of that kid who was killed by the bullies was NOT LEGALLY guilty of any crime. Being a bad friend, being racist, being a jerk are NOT legally crimes and at the end he was facing legal action for not reporting the crime either. No way he would be convicted.
1. He TRIED to protect his friend, but he was a victim too, the bullies restrained him when he was trying to save his friend.
2. The bullies THREATENED him, that is a VERY COMMON tactic, happens a lot in places where criminal gangs run rampant, witnesses often do not come forward out of fear and many states have even passed laws to protect frightened witnesses.
So when all is said and done his ONLY crime is being the witness to a crime that he actively tried to prevent but was completely unable to and delaying for a long time reporting it out of a genuine fear of retaliation, COWARDICE basically. He was in NO LEGAL DANGER.