I am not a lawyer, but I think you have seen in the news cases of people who went to the police to report a robbery and these people were not of American nationality, so if you or anyone else was stolen by someone who lives in the USA or stolen by a company that is in the US, you can report the US police to solve your problem.
or make this case FBI?
I do not know what are the cases that the FBI has jurisdiction to investigate something, this is something that you should consult a lawyer
I'm not an attorney, but it's fairly easy to research this. First, Bittrex is a company that is registered in Redmond, Washington. So the state of Washington is one jurisdiction, and the city of Redmond, WA is another. In the state of Washington, it's possible to bring criminal charges against a corporation, but you must convince a state prosecutor to bring the charges. That would be done by contacting the Washington State Office of the Attorney General. In general, this sort of thing is not done without legal representation. Meaning, basically, as skmdrony says above ... get a lawyer. If you can somehow show an attorney that you have $10 million tied up, I would be very surprised if you couldn't find one to work on a contingency basis.
Of course, I am not an attorney and this is NOT PROFESSIONAL LEGAL ADVICE .. it's just some common sense from someone who happens to live in the Unites States and used to live in the state of Washington.