In King, Maryland police took a DNA swab of Alonzo King during his arrest. The police then ran his DNA against a database, matched it to evidence from an unsolved rape, and used that match to charge and convict him. King appealed his conviction, arguing that the warrantless DNA swab violated his Fourth Amendment rights.

The Supreme Court disagreed by a 5-4 vote. Collecting the DNA of defendants upon arrest, argued Justice Anthony Kennedy in his majority opinion, is no different than photographing and fingerprinting them. “The legitimate government interest served by the Maryland DNA Collection Act is one that is well established: the need for law enforcement officers in a safe and accurate way to process and identify the persons and possessions they must take into custody,” he explained. Chief Justice John Roberts, and Justices Clarence Thomas, Stephen Breyer, and Samuel Alito, agreed.

Kennedy’s majority opinion prompted a thundering dissent from Justice Antonin Scalia, who joined with Justices Ruth Bader Ginsburg, Sonia Sotomayor, and Elena Kagan. “It is obvious that no such noninvestigative motive exists in this case,” he shot back. “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.”

Scalia’s dissent thoroughly gutted the majority’s logic. Central to Kennedy’s argument was the assertion that collecting King’s DNA helped identify him, thereby avoiding “inordinate risks for facility staff” or “existing detainee populations.” Scalia countered by quoting the statute itself, which prohibited testing arrestee DNA before the first arraignment date. Moreover, he asked, “Does the Court really believe that Maryland did not know whom it was arraigning?”

Yes, Scalia noted, Maryland’s DNA-collection statute could help solve crimes—but that doesn’t justify violating an arrestee’s Fourth Amendment rights. “No matter the degree of invasiveness, suspicionless searches are never allowed if their principal end is ordinary crimesolving,” he declared. He also nodded to the law’s more sinister implications in the aggregate. “Perhaps the construction of such a genetic panopticon is wise,” Scalia concluded. “But I doubt that the proud men who wrote the charter of our liberties would have been so eager to open their mouths for royal inspection.”

Many of Scalia’s themes would resurface in another Fourth Amendment case two years later. In Riley v. California, a California police officer stopped David Riley for expired registration tags, then impounded his car for a suspended license, and finally arrested him for concealed firearms found during an inventory search of the car. What happened next triggered the eventual Supreme Court case. During the post-arrest search, officers searched Riley’s cellphone without a warrant and found photos that seemed to link Riley to other recent crimes.