You will need a legal help on this one.

First of all, is he a student? You might want to reach out to his school and see if the Foreign Student department can help. If its a big UNI, they might have a law department. I know this way the school will know of his arrest, but if he is not guilty of anything then he shouldn't be worried.

If he is not a student, you might want to reach out to a lawyer. If money is the issue then see if there is a non-profit legal advisary group in the area. Telephone consultation is free for many lawyers, so may be you can even call some lawyers.

It's strange that he got jailed for not willing to pay alone. Are you sure you have the full story?