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.ADDED: Orin Kerr notes that "Justice Scalia has been on the defense side of every non-unanimous Fourth Amendment case this term:"
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.
King (today’s case in which he wrote the dissent), Bailey (in which he joined the 6-3 majority), Jardines (in which he wrote the majority), and McNeely (in which he joined the Sotomayor plurality/majority opinion). In contrast, Justice Breyer has been on the government’s side in each of the Term’s non-unanimous Fourth Amendment cases: King (in which he joined Kennedy’s majority), Bailey (in which he wrote the dissent), Jardines (in which he joined the dissent) and McNeely (in which he joined the more government-friendly Roberts concurrence/dissent with Alito).