Habeas corpus, the legal procedure that keeps the government from detaining someone indefinitely without cause, was not suspended in 2001 and remains intact for U.S. citizens. However, non-citizens suspected of terrorism may in some cases be held indefinitely without trial.
The Constitution states that this right may not be suspended except "when in cases of rebellion or invasion the public safety may require it."
A Georgetown Law report found that under Section 412 of the Patriot Act, the government may subject non-citizen terrorist suspects to "potentially indefinite detention" when, as the Department of Justice stated, "releasing the alien will threaten national security or cause harm to the community or any person." Because the Patriot Act grants the government broad judgement authority on these fronts, it severely limits courts' ability to assess the merits of detention.