I concur with the consensus. He should have gotten rid of him. Not only would he sell people into slavery, but he also is willing to kill people in cold blood for some profit. Such people have to be taken out. Either by throwing them into jail or ..., well I don't want to sound too edgy, but If they can't be handled in any other way and they continue to pose a thread, by killing them. (Only as a last option.) Indefinitely locking them away is preferable. I would also settle for "Destroying his ability (not locking it, I mean destroying it)". But in the end they just left him...
As a cherry on the top, he does know now, that magical laws ain't working on MC. Another information, that surely won't work against MC. I know I shouldn't, but I hope MC will pay for it somehow. But I also know, that in that case he will only pay indirectly, because somebody else will pay the price for his nice, guiltless night's rest.