“I do not recall the Viet Cong asking me if I was a natural born or Naturalized American before they shot at me, they just shot at all of us “ f107HyperSabr
The Constitution supersedes any treaty in matters of American law.
Ergo, the Constitution applies and the Geneva Conventions do not when it comes to the treatment of American citizens by American authorities.
The supremacy becomes explicit later in the Article, since it says judges are not bound by treaties in any instance where said treaties contradict the Constitution or federal law.
I see no reason why this man, even if he in fact is planning to kill Americans, should be treated any different.