The Department of Defense has confirmed that an (as-yet-unidentified) American citizen is being held in U.S. military custody in Syria or Iraq as an enemy combatant. More specifically, the available information asserts that he was a fighter for the Islamic State who was captured in Syria by U.S.-friendly forces (or at least surrendered to those forces), and was then turned over to the United States.
How significant is this development from a legal perspective?
The straight civilian prosecution option: Under this option, the individual will be brought back to the United States to face civilian criminal prosecution as rapidly as possible. This option would minimize the legal and political friction that will arise under the other options mentioned below. If the individual was indeed an Islamic State fighter, and there is admissible evidence to that effect, there will be ample charging options (material support, conspiracy, and others).
The straight military detention option: The individual might be kept in military detention under color of the law of armed conflict, as an enemy combatant. We have not had a situation like that (long-term military detention with a citizen) for many years. It happened previously with José Padilla, of course, and Yaser Hamdi. Hamdi’s case seems particularly relevant as an analogy, insofar as both cases involve a U.S. citizen said to be a fighter for an enemy force in an overseas location at a time and place when and where it is quite clear that the law of armed conflict applies. The Supreme Court concluded in Hamdi’s case that his citizenship did not relieve him from being subject to military detention in such circumstances, so long as the government could prove he was in fact the person they claimed him to be (since as a citizen he had Fifth Amendment due process rights), and so long as the underlying state of armed conflict continued (with qualifications relating to the possibility that the conflict might evolve in murky ways warranting renewed attention down the road). Then again, Hamdi can be distinguished from this particular individual in that the 2001 authorization for use of military force relatively clearly covered the Afghan Taliban, whereas the relevance of the 2001 authorization for use of military force to the Islamic State is a contested question that courts have never addressed. If this individual is held as an enemy combatant long enough for the machinery of habeas review to get underway — and surely the…