When Dzhokhar Tsarnaev was arrested after a firefight with the police and then a dash into the darkness that ended with him curled up in a backyard boat, there was criticism from both sides of the legal/political spectrum. First, Sen. Lindsey Graham was incensed that Tsarnaev's detention was being handled by the civilian criminal justice system. Graham wanted him labeled an enemy combatant and held in military custody. Phrases like "the War on Terror" crept into the discussion sparked by Graham's demand, and there were plenty of commentators who agree with Graham that Tsarnaev's detention was a matter of national security for the military to run.
On the other side of the spectrum, the Administration quickly distanced itself from Graham's suggestion. In making the point that the case should be handled by the domestic criminal justice system, White House spokesman Jay Carney noted two seemingly crucial facts: Tsarnaev was an American citizen, and he was captured on U.S. soil. Apparently these two facts indicated that the civilian process -- not a military one -- was required for Dzhokhar Tsarnaev.
I think both sides of this debate got it completely wrong. Graham was wrong because there was no reason for military detention here because the operation had nothing to do with an armed conflict. On the other hand, the Administration also got it wrong by appealing to citizenship and location -- two factors which are not determinative of the matter. Let me explain more why I think both sides are wrong on this.
First, as to U.S. citizenship. Under the laws of war, citizenship confers no immunity from military detention (as long as military detention is authorized by some legal norm). Indeed, citizens are sometimes detained in non-international armed conflicts (NIAC), as they were during the U.S. Civil War. Second, as to territory, the geography of the detention is also not fully determinative. Although the United States is not accustomed to engaging in armed conflict within the borders of the homeland, this is a contingent fact of our relative security, not a legal necessity. In other words, if fighting were to come to the shores of the United States, the laws of war would still apply in those situations.
That being said, I happen to agree with the Administration that Dzhokhar Tsarnaev could not be subject to military detention, although for completely different reasons. The correct reason is that Tsarnaev is not a member of an armed group with which the United States is engaged in an armed conflict. Although facts are still being gathered, at this moment in time there is no publicly available information to suggest that Tsarnaev is a member of Al-Qaeda or any other group that is currently engaged in an armed conflict with the United States. And that's the relevant issue here. Military detention is triggered by the laws of war, which itself is only triggered when there is an armed conflict between parties. The location or the citizenship of the detainee just is not relevant for international law.
Now, you might ask whether there are additional constitutional protections that apply in the territory of the United States? You might think so, although the leading case regarding detention of U.S. citizens, Hamdi v. Rumsfeld, largely drew upon the international laws of war to provide the content of the constitutional due process rights that Hamdi was owed. Furthermore, in Boumediene, the Supreme Court extended many of those same principles to non-U.S. citizens, further suggesting that citizenship lacks great constitutional significance in this area.
(U.S. statutory law is a different matter. Congress can limit the jurisdiction of military commissions to non-U.S. citizens if it wants.)
What about territory? Hamdi involved the capture of a U.S. citizen in Afghanistan, and the case did not address what level of due process protection would be required if the government were to capture a combatant within the United States. However, in Quirin, the Nazi saboteurs were captured within the United States, and the Supreme Court upheld their detention and military trial (and eventual execution). The Supreme Court might have addressed this question more squarely in Padilla, though the Bush Administration voluntarily transfered Padilla to civilian court, and put him on trial in Florida, rather than risk a negative outcome before the Supreme Court on this question.
All of this is just to emphasize that both sides need to be asking the right questions. Citizenship and territory aren't so relevant here. The bigger question is whether Tsarnaev is a member of an armed group with which the U.S. is engaged in an armed conflict. If he is not, then there is simply no basis to trigger military detention (or a military tribunal).