Payback are always a possibility over revenge on United States Government but the security are already fortified all over the world over this issue.
I do not think this is part of the "payback" or Revenge on 9/11 but justice stood over him and will bring good morale against the terrorist and the terrorist will demoralize over his death.
Yeah, agree with the above statement, But my "proper authority" for me is Allah S.W.T. Himself to judge him for what he have do!