Have your CPS person or you can go to the school and explain that there is an investigation into XDH and his handling of DS. Get the school to note down DS's attitude re his dad and when he comes back from his dad's. If the school has to actively watch DS to monitor his moods then they might see some corelating evidence against XDH. Find out if the school has a counsellor and ask to speak to them and see if they can do anything. If CPS is ready to proceed against your XH but are waiting to hear what your son says in counselling then you would think they would fast track him. Then I would be warning the school of their duty of care toward your son.