After reading the US Supreme Court cases on Gitmo and their interpretation of the laws the Democratic Congress passed on holding terrorists, I haven't a clue as to what is legal or illegal, much less 'unquestionably so.  Between the multiple holdings and the multiple dissents on everything about this situation and the rights or lack of rights, depending on everything as to where they were captured and even whether we keep troops in Afghanistan or not, I wouldn't make any bets on anything about this.  Except that the Congress as of today refuses to provide any money to move anyone anywhere into the US.