My son knows all the kids involved. The investigation concluded that your son drew the swastika on a desk then blamed it on another child. Then your son turns around and says that the other child and 2 other kids were "bullying" him. The accusations were unfounded because it was determined that your son lied so he wouldn't get in trouble. Making excuses for your child will only make things worse for him. 
I'm glad your son is leaving because this isn't the only incident your son has been involved in, which includes physically assaulting and harassing other kids. Perhaps you should look at your child first before calling another child a "bully". Like I said earlier, making excuses for your child will only make things worse.