Although few noticed the link between them, two Supreme Court cases decided in the same week last Term, Ashcroft v. al-Kidd and Camreta v. Greene, both involved the Fourth Amendment implications of detaining witnesses to a crime. Al-Kidd, an American citizen, was arrested under the federal material witness statute in connection with an investigation into terrorist activities, and Greene, a nine-year-old suspected victim of child abuse, was seized and interrogated at school by two state officials. The opinions issued in the two cases did little to resolve the constitutional issues that arise in witness detention cases, and in fact muddied the waters by suggesting that the motivations underlying the decision to seize a witness are constitutionally irrelevant. In fact, however, the Fourth Amendment doctrine that governs these cases is the special needs exception, which under Supreme Court precedent does trigger an inquiry into subjective motive. As a result, the Fourth Amendment was violated if al-Kidd was pretextually detained because the FBI wanted an opportunity to investigate him, but lacked the probable cause to arrest him, or if the primary purpose for seizing Greene was to generate evidence in connection with the criminal charges pending against her father.