According to Charlie Savage in today's New York Times, this is a question in hot interagency dispute this week. The basic concern of course is that (i) the D.C. Circuit's ruling in Hamdan II amply foreshadows that the Circuit will reject the viability of conspiracy as a stand-alone charge for pre-2006 conduct (on the theory that the Hamdan II panel adopted a sort of clear-evidence rule pursuant to which the commission system's capacity to prosecute for pre-2006 conduct encompasses only charges that relatively clearly at the time constituted violated international law) and (ii) the prospects for reversal by the Supreme Court are at best thin given what was said on the subject in 2006's Hamdan I SCOTUS ruling (four justices expressly rejecting the viability of conspiracy charges, and Justice Kennedy keeping his cards very close to his vest on the subject). In short, a dark cloud is looming over the use of conspiracy charges on a stand-alone basis for pre-2006 conduct, and though rain is not literally inevitable it is highly-likely.
In such circumstances, is it better for the government to fight to the last, knowing that it will lose in a high-profile manner before the DC Circuit sometime quite soon but then hoping that a closely-divided SCOTUS will reverse in a decision that most likely would not arrive until early 2014? Or instead should the government abandon the charge now, gaining at least some degree of credibility and enhanced legitimacy for the remainder of the system while also preserving the option to charge conspiracy in cases involving post-2006 conduct (should such cases exist or arise) and perhaps even preserving the option of using conspiracy or something like it not as a stand-alone offense but rather as a theory of liability linking persons to other, completed crimes? This is, I think, an exceptionally difficult question, and I do not envy those who are charged with resolving it. That said, it seems to me that the latter option is the wiser of the two, in part because I think the legitimacy gains it offers are genuine and important, and in part because I rate the government's chances of eventually prevailing on the merits issue relatively low.
That said, one big factor that is not actually clear to me is the extent to which abandoning conspiracy (and, I should add, declining to pursue an appeal of the Hamdan II decision itself, and thus completely the demise of the material support option for pre-2006 conduct) is the extent to which this will deal a fatal blow to any existing case. There are both qualitative and quantitative elements to that inquiry. Quantitatively, it would of course be interesting to know just how many cases there are, or are likely to be, in which the case absolutely depends on these charges. But knowing that number alone isn't enough. It would help as well to understand just how important those particular defendants might be. One can imagine that there might be many cases that could be brought that would depend on conspiracy or material support grounds, yet those defendants might by and large be small fry. Conversely, one can imagine that only a few cases or potential cases would be impacted, yet those defendants might be big fish. In that regard, as Charlie's story reminds us, it does not appear that the 9/11 prosecution itself would be mortally wounded by the demise of these charges. That's an important part of the context here, at any rate.