Retain an immigration attorney who is familiar with criminal law, there are multiple issues and will need to be cleared up before any attempt at bringing him to the US legally, good luck.
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You cannot clear up the warrant by appearing in court for him.
As it appears the warrant was issued by mistake, it might be possible for an attorney who is quite familiar with the court and its staff to ask the court to recall or clear the felony bench warrant without his appearance due to the clerical error. It is certainly well worth a try, as right now, if he is stopped once back in the U.S., he might be detained.
You must understand that normally, if one is charged with a felony, as it appears he was, an attorney cannot appear on behalf of a defendant. Here, however, the bench warrant appears to have been issued in error.
Best of luck.
Immediately consult with an immigration lawyer in your area who is also familiar with criminal law. He or she will explain to you what needs to be done (and will do it too.)
Behar Intl. Counsel 619.234.5962 Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.