The Supreme Court’s 5–4 decision today in Maryland v. King produced an unusual split. Justice Scalia’s colorful dissent was joined by Justices Ginsburg, Sotomayor, and Kagan; Justice Kennedy wrote for the Court, including for Justice Breyer. But it also brought to the fore some of the difficulties of interpreting and applying the Fourth Amendment’s protections against unreasonable searches and seizures, where the facts of a given case play so large a role. It’s no accident that such cases are so often before the Court.

Here the main facts were fairly straightforward. Alonzo King was arrested in 2009 on an assault charge. At booking he was photographed and fingerprinted. And the police took a cheek swab for DNA testing, pursuant to a Maryland statute aimed at, among other things, law enforcement. Subsequent testing of the DNA sample enabled the police to link King to an unrelated, unsolved 2003 rape, for which he was subsequently tried and convicted. King argued that the police had no probable cause to believe that he had committed that 2003 crime and therefore had no basis for conducting the DNA search that ultimately linked him to it. The Maryland Court of Appeals agreed and threw out the evidence. The Supreme Court reversed that decision, holding that the DNA search was “reasonable” under the Fourth Amendment.

Without going deeply into the competing arguments, Scalia makes a powerful case that the Court’s decisions, as they have evolved under myriad factual circumstances, are on King’s side: In particular, the Court has never allowed suspicionless searches for law enforcement purposes. And his arguments against the majority’s claim that the DNA sample was taken for purposes of identification are devastating. In fact, as he says in a footnote, “Why not just come out and say that any suspicionless search of an arrestee is allowed if it will be useful to solve crimes?” The Court would indeed have been more honest if it had said that.

But Scalia’s argument is weaker when he goes after a point on which the Court relies most heavily, the similarity between the police use of fingerprints and, as here, a DNA swab. The Court has never offered a “ready answer” to the question whether taking a person’s fingerprints is a search, he says. That is done “primarily to identify” the person – “though that process sometimes solves crimes,” he adds. Well, if that’s so, then perhaps, if pressed, he might also find that fingerprints could not be used for “law enforcement purposes.”

These Fourth Amendment cases are often close calls, not least because the jurisprudence surrounding the amendment’s warrant requirement has often been the tail that wags the “unreasonable” dog, which makes for a counterintuitive result in some cases. At the least, however, if the Court is going to revise its ever-evolving precedents, it should say so clearly. Today’s decision does not do that, and Scalia rightly calls the majority on it.