My quess is that that individual will probably be detiened at entry and place in removal proceeding. He will probably have to got to jail and after complying with his sentence he will be deported. I belive he will also trigger a bar to enter to the US for a few years. It could be betweed 3 to 10 years bar. Not really sure, it depends on the offense that he committed. I would suggest contacting legal advice from an experience immigration attorney soon.
Information in this post is not the same as legal advice :no: I recommend you consult a lawyer if you want professional assurance that this information, and your interpretation of it, is appropriate to your particular situation.