@ayiddisheneshomaiscrying – My heart goes out to you and your son. I agree with jewishfeminist that you should tell your son that you’ll believe him no matter how far-fetched his account sounds. It could be someone close, but I’m not jumping to blame his father or anything like that. I applaud both of your boy’s parents for doing your best to help him recover from this appalling trauma.
Perhaps he was threatened with further harm if he identified the perpetrator? Bullies work that way. Just because the perpetrator is exposed and IY”H immobilized doesn’t mean he or she doesn’t have lackeys who might try to cause further harm. And lackeys could be retaliating school staff, students, or in general, friends of the perpetrator.