Not in Pennsylvania, so others might know more. But for me, it would help to see the language in the NOREP as to what was agreed to at the meeting. Regardless, however, it looks like you were given some bad advice during the meeting from individuals who did not understand the entire process or know all the facts in your case. Under the board policy, you appear to be out of luck. My suggestions are:
1. Ask for all policies regarding ability to transfer schools. There might be some other way to request a transfer.
2. Write a letter to the superintendent and school board members pleading your case. Since you don't have any policy or legal ground to stand on, appeal to their emotions to make an exception. However, there are a couple of legal issues you could allude to (but I would start out nice and not demanding in this initial letter/email). State how this would affect your son and his ability to access his education (he would be so traumatized he wouldn't be able to focus and learn - I would even suggest getting a letter from a psychologist/psychiatrist stating the environment would making learning difficult, if not impossible, and attach the letter). Hopefully they could connect the dots that they would be denying FAPE. Another legal angle would be adding something like "it would be be devastating to my son physically, mentally, and emotionally if another attack were to occur." Hopefully they could connect the dots in terms of their liability if an attack occurred and they were on notice of the previous one.
3. If they insist on knowing the other boy's name, keep in mind that the school district is required to keep this confidential.