Citizens, Combatants and the Constitution
The Geneva Conventions and our Constitution make clear that any member of an enemy force with which we are engaged in armed combat may, upon capture, be held in military confinement for as long as hostilities persist. But the rationale for such imprisonment is narrow: it must be strictly to prevent a prisoner from returning to the war against our nation and its people. (Secretary of Defense Donald Rumsfeld's assertion that the United States is holding Mr. Padilla because it is "interested in finding out what he knows" is not legally persuasive.)

The administration cites court decisions from 1942 and 1946 in support of military detention of enemy combatants who are United States citizens. But there's an obvious point worth noting: these decisions arose only because the federal courts were considering the constitutional claims of the detainees in the first place. In both cases the courts upheld military jurisdiction, and in a justly infamous 1944 decision the Supreme Court upheld the evacuation of Americans of Japanese ancestry from their communities. But the court, in a little-remembered decision issued the same day, also held that the continued detention of Japanese Americans — absent any proof of disloyalty — was illegal.

For our government to retain its legitimacy, its conduct must always be subject to challenge in a court of law. Nor can this judicial review be an empty gesture; lawyers must be allowed ample access to those the government would detain. It is the threat — and the promise — of judicial intervention that keeps executive power from veering into tyranny.
http://www.nytimes.com/2002/06/16/opinion/16TRIB.html