I can only say that, at first glance, you appear to have the right to claim the child because:
The IRS defines the term "Custodial Parent" Differently than Legal or Courts would define this term. According to the IRS what makes you the Custodial Parent is that the child resides with you for more than half the year...period. So, let's say that the father had the child stay with them from Jan. 1st of the tax year to July, and then, the child returned to your care, as per an agreement or court order or for whatever reason....then He would be considered the Custodial Parent for tax purposes, despite you having been awarded full custody by the legal system. There is one exception to this rule - see, "Kidnapping Rule" for the IRS. Now, since the child resided with you for the whole year, you are considered the Custodial Parent for Tax purposes. Hope this helps.
🙂
