[JURIST] The US Supreme Court [official website] ruled [opinion, PDF] Wednesday in Missouri v. McNeely [SCOTUSblog backgrounder] that the Fourth Amendment [text; Cornell LII backgrounder] may require a warrant for a blood test in a drunk-driving investigation. The divided court ultimately held that “in drunk-driving investigations, the natural dissipation of alcohol in the bloodstream does not constitute an exigency in every case sufficient to justify a blood test without a warrant.” Delivering the opinion in Parts I, II-A, II-B, and IV, Associate Justice Sonia Sotomayor wrote that, while a warrantless search of a person is reasonable if it falls within a recognized exception of the law, the state’s argument that the existence of probable cause constitutes a per se exigent circumstance must be rejected. Sotomayor reasoned that when officers performing a drunk-driving investigation “can reasonably obtain a warrant before having a blood sample drawn without significantly undermining the efficacy of the search, the Fourth Amendment mandates that they do so.” She further reasoned that Missouri did not argue the existence of any exigent circumstances with regard to the drunk-driving investigation at issue; rather, because the State sought the imposition of a broad, per se rule, the record did not provide the court “with an adequate framework for a detailed discussion of the relevant factors that can be taken into account in determining the reasonableness of acting without a warrant.” Sotomayor also delivered the court’s opinion with respect to Part III, where she and Justices Antonin Scalia, Ruth Bader Ginsburg and Elena Kagan rejected Missouri’s argument for a case-by-case approach to determining whether exigent circumstances exist. Justice Anthony Kennedy filed an opinion concurring in part, while Chief Justice John Roberts, joined by Justices Stephen Breyer and Samuel Alito, filed an opinion concurring in part and dissenting in part. Justice Clarence Thomas filed the court’s only full dissent.

The Supreme Court heard oral arguments [JURIST report] in the case in January. The dispute arose out of the arrest of Tyler McNeely in the rural Missouri county of Cape Girardea [official website] in October 2010. McNeely was pulled over by a state policeman after the officer observed McNeely’s car cross the yellow center line of the roadway three times. After noticing that McNeely’s eyes were red and glassy and that his breath smelled of alcohol, the officer administered several field sobriety tests. McNeely performed poorly on four of the tests and refused to submit to a portable breathalyzer test. The officer then arrested McNeely for driving while intoxicated and brought him to the hospital for a blood sample. Although the state policeman read McNeely the Missouri Implied Consent statement [official backgrounder], McNeely still refused. The officer then ordered the sample to be taken anyway, which revealed McNeely’s blood alcohol content to be 0.154, nearly double the legal limit of 0.08. After Missouri charged McNeely with driving while intoxicated, the trial court granted the defendant’s motion to suppress evidence of the warrantless blood sample. On appeal, the Missouri Court of Appeals ruled that the trial court erred, and transferred the case to the Missouri Supreme Court [official websites]. There, in January 2012, the trial court’s opinion was affirmed [opinion].