The Justice Department today released John Yoo's 2003 torture memo to Congress. This is the infamous memo that the Bush Administration relied on in justifying it's "harsh interrorgation techniques" on prisoners overseas. This was the memo that was in force when the Abu Ghraib detainees were subjected to cruel treatment and torture.
Part One of the memo is here, and Part Two is here (pdf.)
Shorter version: Yoo wrote the Constitution is not in play.
In the March 14, 2003 memo, Yoo says the Constitution was not in play with regard to the interrogations because the Fifth Amendment (which provides for due process of law) and the Eighth Amendment (which prevents the government from employing cruel and usual punishment) does "not extend to alien enemy combatants held abroad.":
The memo goes on to explain that federal criminal statutes regarding assault and other crimes against the body don't apply to authorized military interrogations overseas and that statutes that do apply to the conduct of U.S. officials abroad pertaining to war crimes and torture establish a limited obligation on the part of interrogators to refrain from bodily harm.
The memo also says the Geneva Conventions don't apply al-Qaida and the Taliban.