In a 5-4 decision handed down today in the case of Maryland v. King, the U.S. Supreme Court held that the 4th Amendment does not prevent law enforcement officials from obtaining and testing DNA samples from individuals arrested for serious crimes. According to the majority opinion of Justice Anthony Kennedy, which was joined by Chief Justice John Roberts and Justices Clarence Thomas, Stephen Breyer, and Samuel Alito, the use of a Q-tip to swab the inside cheek of an arrested suspect "is 'no more than an extension of methods of identification long used in dealing with persons under arrest,'" such as fingerprinting, and therefore constitutionally permissible. "In the balance of reasonableness required by the Fourth Amendment," Kennedy's opinion continues, "the Court must give great weight both to the significant government interest at stake in the identification of arrestees and to the unmatched potential of DNA identification to serve that interest."

Writing in dissent, Justice Antonin Scalia, joined by Justices Ruth Bader Ginsburg, Sonia Sotomayor, and Elena Kagan, strongly rejected the majority's reasoning:

The Fourth Amendment forbids searching a person for evidence of a crime when there is no basis for believing the person is guilty of the crime or is in possession of incriminating evidence. That prohibition is categorical and without exception; it lies at the very heart of the Fourth Amendment. Whenever this Court has allowed a suspicionless search, it has insisted upon a justifying motive apart from the investigation of crime. It is obvious that no such noninvestigative motive exists in this case. The Court's assertion that DNA is being taken, not to solve crimes, but to identify those in the State's custody, taxes the credulity of the credulous. And the Court's comparison of Maryland's DNA searches to other techniques, such as fingerprinting, can seem apt only to those who know no more than today's opinion has chosen to tell them about how those DNA searches actually work.

The Supreme Court's opinion in Maryland v. King is available here.