Except, of course, that it is. Because we all know--and indeed the facts of the case squarely presented--that the purpose of the DNA swab isn't to identify the prisoner; as Justice Scalia made clear in his superb dissent, the purpose of the DNA swab is to use the DNA to investigate whether the prisoner may have been guilty of other crimes of which the State has no reason to suspect him of having committed. Scalia refuses point-blank to accept the argumentum excrementum taurorem that the swab is solely for identification purposes:
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.I have long maintained that from 1986 to 2000, Scalia was "often an ornament of the Court," having by and large been genuinely engaged in a principled effort at an originalist jurisprudence--not one I often agreed with, but intellectually consistent and worthy of respect. His return to form is most welcome.
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
As to Justice Breyer joining this disingenuous majority opinion, I'll outsource my commentary to Kevin Kline:
Kidding aside, in the second edition of First Amendment, First Principles (2004), I noted the disappointing tendency of Justice Breyer to explicitly balance away constitutional rights in favor of his preferred policy outcomes. This is just one of a series of his living down to this description, I'm afraid.