Try him for sedition. Use teh Nazi camp guards as precedent for denaturalizing him. We should deport the guy ASAP.
It will not fly, and is pointless anyway. Instead, make him useful. Read and ponder the following Sun Tzu paragraph: "a wise general employs all kinds of people - clever and stupid, greedy, brave and cowardly. He uses the brave people on the battlefront; he uses the clever people in his council, for they exult in providing advice; he uses the greedy ones, for they are good at seizing an advantage; he uses cowardly people, for they are good in extricating themselves from difficulties; and he uses the stupid ones, for they are not afraid of death". [quoted from memory]. Ditto in the statecraft, not only in strategy. Make him useful.