On Monday, the Supreme Court ruled 8-to-0 that John Ashcroft cannot be held personally liable for alleged abuse of material-witness detention powers. (Justice Kagan recused herself because of her involvement in the case as U.S. Solicitor General.)

In the case of Ashcroft v. al-Kidd, Abdullah al-Kidd contended that he was illegally held in high-security prisons as a material witness in a terrorism investigation for 15 days. He claimed that the Federal government had a policy of using U.S. Code Section 3144, which gave it the power to detain material witnesses to a crime, as a pretext for holding suspects when they otherwise did not have evidence to do so.

The Court ruled unanimously that al-Kidd did not have grounds for a lawsuit, as there was no clearly established law prohibiting the government’s actions, and that al-Kidd didn’t challenge the validity of the warrant, only its application. The Court split 4 to 4 over whether the government’s use of Section 3144 does not violate the Fourth Amendment to the Constitution, however. Justices Kennedy, Ginsburg, and Sotomayor filed concurring opinions (joined by Justice Breyer) stating that the constitutionality issue was still an open question.

Given that Justice Kagan would be more likely to side with the other liberal-leaning justices if a direct challenge to the U.S. policy makes it to the Court, the debate over the government’s use of material witness detentions as an antiterrorism tactic is far from over.

To read more about the case, including oral arguments, the lower-court decision and brief excerpts from both sides, see the April issue of Supreme Court Debates.