He most likely went somewhere he wasn't supposed to be and he witnessed crimes committed somewhere in that building. Crimes could be any number of things and he may not even been able to understand the legality of what he came across.  Bottom line they couldn't let him leave knowingly or unknowingly having been a witness and a lose end to the operators over there. They brought that kid as close to death as possible without killing him before he was handed over with the IQ of a potato.  He should have stayed with the group. Had he known what it could lead to he would have.  Trump saying Kim didn't know is telling of who would be left. Either DS or Kim's people under the order of the DS.  Rearranged teeth could be electro shock used with something non-giving to bite down on. They really put the works on that kid.