Dependent claimed already by ex, what's the best strategy for me in filling mine?

[mperez2011tax]

So yes my return was rejected bc my ex claimed our son on his return 1st. He did so falsely though because he doesn't even live in the same state. Our son is with me 365 unless he does go visit  dad for 1-2 weeks in the summer, and he is disabled. As I understand the process now, I have to paper file my return (causing delays for my refund & stimulus). Then the duplicate use of his be SSN will get flagged, the a letter will be sent to us both (further delay), and then an investigation could be opened (delay, delay), then the irs will send another letter to request us for proof (It's literally Halloween by now), I'll send my proof (don't know that dad dad has any)... (snail mail during the holidays=more delays), proof has to be reviewed and THEN I'll finally be approved for the claim, but then wait again for the refund AND my stimulus. I'll be lucky if it can wrap up by end of summer, but doubt it.

My question is, Idk either logical or really stupid... shouldn't I just write an explanation of my right to the claim and send in documents needed to prove that ALONG WITH my return when I paper file? Wouldn't that eliminate the need for all the back & forth & time to investigate?

Is there any form to use or is there any law that says I can't send these documents (Birth cert, school docs, SSI papers, etc.) with my  return forms? 

[macuser_22]

If a dependent that you are entitled to claim has already been claimed by another taxpayer, your e-filed return will reject since the child's SSN has already been used (either intentionally or in error such as a mistyped SSN).

Your only recourse is to file a correct tax return, claiming what you are entitled to claim, then print and mail the return.

The IRS will process both returns and pay any refunds. Shortly (within a year) the IRS will mail letters to both taxpayers asking if their tax return was filed in error and suggesting that they amend if they improperly claimed the child.

If neither taxpayer amends, the IRS will send a second letter asking for each taxpayers proof that they are entitled to claim the dependent, such as proof that the child physically lived with them more than half the year. School records, child care records, household receipts, medical bills, etc., that show that the child lives with you should be retained.

The IRS will evaluate each taxpayers claim and award the dependent to one taxpayer, the other will have to payback any refund received plus interest and possible penalties. The parent that had physical custody usually always wins.

Do not ignore the letters or you will loose.

[mperez2011tax]

@macuser_22  thanks for the info. It's so complicated, but didn't know I'd get a refund before an investigation. But it'll still be a lot of work for him to amend, me to paper file and deal with this down the road again. Plus I don't want him in trouble we just never discussed how we'd proceed after he moved. I think we're in agreement that he'll keep his return as is and claim the child exemption, I'll do that form 88## & adjust mine, since I haven't filed yet. I'll take the child earn income credits & keep HOH status. Then he said he'll give me a percentage of the difference of my refund for not claiming our son and the $500 stimulus he already received for him. And we'll write a new agreement for me to claim from now on and file it as an amendment. He said it's the best way since he's filed & gotten the refund already.