I'd start your legwork here with a phone call to your nearest FBI field office. Make sure you have the paper trail showing from your end you sent crypto to the perpetrators, and ask what the next step would be for claiming your defrauded property. It may also be worth consulting with a lawyer to see what your legal recourse might be here.
Fair warning: there may be no next step. I have no idea if the US government even considers cryptocurrency "property" in any legally-meaningful sense.