As Raff notes, the Washington Post has an editorial this week drawing attention to the important case of Ali Mussa Daqduq, the Lebanese Hezbollah commander who entered Iraq to participate in the insurgency, who allegedly orchestrated the execution of captured American soldiers (among other things), and whom we have continued to hold in military custody in Iraq even as we have wound down the rest of our detention operations. The question at hand is what to do with him. The editorial comes down in favor of a military commission prosecution, rather than turning Daqduq over to the Iraqis for prosecution (though that is what we have done for years, in the vast majority of insurgency-related cases) or civilian criminal prosecution (something we've done only one time with a former insurgent, in a case in which we could only get custody of the person in the first instance if we agreed to use civilian criminal prosecution (the Delaema case, in which the defendant was in the Netherlands when captured)).
A commission trial probably is the best option for this particular case, if (and this is a big if) the Office of Military Commission prosecutors are confident they can prove Daqduq's involvement in the execution of captured soldiers. That would present a conventional war crime offense, subject to little or no complaining about the fundamental legitimacy of the charge.
If the prosecution could only be confident about proving Daqduq's involvement in IED attacks on soldiers in the field, however, it is not as clear that a commission would be the best option. Such attacks unquestionably violate Title 18 and can be prosecuted in civilian court. But to prosecute them in a commission setting presumably would require application of the MCA 2009's terrorism, material support for terrorism, or murder in violation of the law of war offenses. All of these charges would be subject to litigation as to their validity (and as to the last option --murder in violation of the law of war--it is not clear to me in any event that the government's current understanding of that provision includes all killings by an unprivileged belligerent). At a minimum, there is some additional litigation risk in opting for the commission route in that case.
Is there an alternative to prosecuting in either forum? The post suggests continued military detention is a possibility:
Because Mr. Daqduq is an unlawful enemy combatant, the laws of war allow his detention until cessation of hostilities. ... The president should consider all options for dealing with Mr. Daqduq. Prosecution in a U.S. federal court should be weighed, as should detention under the laws of war.
This probably is not an option, however. While it is true that it is extremely difficult to specify the moment when hostilities cease (thus terminating the law of war foundation for continued detention without charge), the United States appears to be on its way out in Iraq (as the shutdown of our detention operations and ongoing withdrawal of forces indicates). It may be that a last minute deal will be struck to keep some forces on in Iraq, and this in turn might provide a hook for sustaining a claim about law of war-based detention authority.
The larger lesson is that the military detention option is an inherently temporary option when it comes to persons captured and held on the ground that we are involved in particular armed conflicts overseas. To hold someone beyond the term of our deployment in that setting, you have to convict them of a crime. Daqduq is the poster child for this point. Unless of course one intends to assert that the United States and Hezbollah are engaged in an armed conflict separate and apart from the armed conflict in Iraq, by analogy to the situation vis-a-vis al Qaeda. But don't hold your breath for Daqduq to be shipped to GTMO or anywhere else on that basis. Habeas litigation would follow, and I frankly cannot imagine the government going to court to argue that its detention authority extends to Hezbollah (the AUMF certainly does not seem to cover that circumstance). I suppose he could be shipped to GTMO simply on the ground that conflict continues in Iraq, that the U.S. continues to have a role in that conflict even as we withdraw, and so forth. That's not an impossible argument to sustain, but it would be quite difficult for the reasons noted above.
From this point of view, prosecution somewhere makes sense. But where to hold him, and which forum to use, is not just a question of the legal merits of each option. There obviously are potentially serious policy, political, and diplomatic implications for extending the GTMO model (detention or commissions) to Hezbollah, however sensible the legal arguments for doing so might be. Lots of moving parts to that inquiry, to say the least.