This week the Supreme Court unanimously rejected a lawsuit by Abdullah al-Kidd, a U.S. citizen who was detained for 16 days in 2003, ostensibly as a material witness, while the government tried unsuccessfully to build a terrorism case against him. Al-Kidd sued former Attorney General John Ashcroft, arguing that he had authorized his subordinates to use the material witness statute as a pretext for preventive detention. Justice Elena Kagan did not participate in the decision because she was involved in the case as solicitor general. But the other eight justices all agreed that Ashcroft was entitled to "qualified immunity" because the pattern of abuse alleged by Al-Kidd (who, like many other "material witnesses" nabbed after 9/11, was never called to testify) was not clearly illegal at the time it occurred.

Five justices—John Roberts, Antonin Scalia, Clarence Thomas, Samuel Alito, and Anthony Kennedy—went further, saying Al-Kidd's Fourth Amendment rights were not violated even if the government was only pretending to hold him as a material witness, provided the statute's formal requirements were satisfied (and assuming the statute itself is constitutional; see below). In a concurring opinion, Kennedy said he's not sure the detention was in fact lawful under the statute. Justices Ruth Bader Ginsburg, Stephen Breyer, and Sonia Sotomayor joined that part of Kennedy's opinion. Ginsburg wrote a separate concurring opinion, joined by Breyer and Sotomayor, that highlighted crucial misstatements and omissions in the statement on which Al-Kidd's arrest was based and the "brutal conditions" of his detention, which belied the pretense that he was being held as a material witness. Sotomayor also wrote a concurring opinion, joined by Ginsburg and Breyer, questioning the majority's position that pretextual detention does not violate the Fourth Amendment and arguing that it was in any case unnecessary to decide that question.

Making the best out of this defeat, ACLU attorney Lee Gelernt, who argued Al-Kidd's case, noted that "half of the justices who participated in today's decision expressed real questions about how the government used the material witness statute in al-Kidd's case." He said he hopes "those questions will lead to a serious examination moving forward of the use of the statute as a tool for preventive detention."

Another cause (pretext?) for hope: In its 2009 decision (PDF) allowing Al-Kidd's suit to proceed, the U.S. Court of Appeals for the 9th Circuit noted that "the Supreme Court has never held that detention of innocent persons as material witnesses is permissible under the Fourth Amendment." It still has not. Because Al-Kidd challenged Ashcroft's abuse of the material witness statute, as opposed to the law itself, the Court did not address the broader question, holding only that "the objectively reasonable arrest and detention of a material witness pursuant to a validly obtained warrant cannot be challenged as unconstitutional on the basis of allegations that the arresting authority had an improper motive." The majority noted that Al-Kidd "does not assert that his arrest would have been unconstitutional absent the alleged pretext."

I discussed the oral arguments in Ashcroft v. Al-Kidd in March.