[jinnamys]

He was arrested on a US common carrier vehicle, bound for the US. This makes him subject to US law - and also means the government is bound by the Constitution to provide access to counsel, due process, etc.

To do otherwise is to head down a very slippery path.

Mukasey appears to disagree....I don't 'know' but after hearing Brennan and reading this, it appears we do have an out that would allow us to hold him outside his ability to get shut down by counsel (according to them).
to wit;

Holding Abdulmutallab for a time in military custody, regardless of where he is ultimately to be charged, would have been entirely lawful—even in the view of the current administration, which has taken the position that it needs no further legislative authority to hold dangerous detainees even for a lengthy period in the United States. Then we could decide at relative leisure where to charge him—whether before a military commission or before a civilian court.