If your son has been arrested than you need a lawyer for your son; they have already made up their mind about the incident and apparently have no interest in any further investigation since they arrested your son. Therefore, at this point he really needs an attorney. There is probably not much that a lawyer is going to be able to do as far as the person making the complaint is concerned; usually, when charges have been filed it is very difficult to make a civil complaint against that person as their allegations have been reviewed and found to establish probable cause for the issuance of the warrant or charges.
I agree with the assessments of Mr Pichlik, and also suggest that you get a lawyer involved immediately to protect your son's rights. Self-help in response to the continued provocation by the alleged victim is not advisable, however the lawyer can deal with the issue through the courts. Good luck.
DISCLAIMER I do not practice law in your State. This answer is provided for informational purposes only. This answer does not constitute legal advice, create an attorney-client relationship, or constitute attorney advertising.