So far I agree with most all of the answers I have read! I'd be curious about the mental health of the biter...does he have a developmental challenge? Obviously the priority is making sure your sons medical and protection needs are in place, but for a youth to bite indicates a greater problem and a potential problem for your son if he gets in trouble and decides to hold a grudge against your son. Bullies rarely recognize they got themselves in trouble...it's always someone else's fault...ugh!
I might talk with the principal and/or school counselor and find out what their strategy is for getting the bully some extra attention in terms of mentoring or programs that work with troubled youth to build confidence and get back on the right track. Bullies, in my experience, are insecure people who exert control where they can because they feel out of control in other situations (i.e., home, emotional regulation, school struggles, etc.). If the school can intervene in a positive and long-term focused kind of way, this benefits everyone, including potential future victims.
I'm not saying the biter shouldn't be disciplined...he needs to be held accountable. And I'm not saying you should take the lead or even play a large role in the bully's solution. I guess I'm just suggesting that discipline for single offenses rarely stops a bully from future bullying and that I would advocate for the school to play a larger role in helping to shape this young man into someone who doesn't feel the need to bully and learns how to thrive instead of instigate problems (he doesn't win for bullying, even if he thinks he does).
Good luck with all of this! It sounds very stressful and infuriating for sure!!!