Is it crime ?單身老貓

I have my daughter's custody. We divorced in China. The court give my daughter's custody to me. I think it is sole custody.
Now my ex said he had my daughter's green card and he didn't want give to me.
Is it illegal he hold my daughter's green card. Can I sue him? Is United States admit divorce document of Chinese too?
What shall I do to stop my ex bother us and he give me my daughter's green card?

Anybody know a good lawyer around Rockville, Maryland area?