Evil regimes and the nature of law

Should those who have acted wrongfully, but authorized by the legal system of an evil regime, be held responsible in legal proceedings after the end of the evil regime? IF those who have so acted with an evil regime are subsequently held accountable , can that accountability be fully under law? In defending your position, make connections to the dispute between positivism and natural law. 

Focus your paper on Lon Fuller's ''The problem of the grudge informer'' 

Must be 6 pages long double spaced in 12pt font with standard margins