California and the Fourth Amendment

On Wednesday, the United States Court of Appeals for the Ninth Circuit is scheduled to reconsider whether California violates the Fourth Amendment’s prohibition against searches and seizures by requiring police to take DNA samples from people arrested but not yet convicted of felonies. California’s law is ostensibly aimed at accurately identifying those arrested, solving crimes and exonerating the innocent. It is also, unfortunately, unconstitutional.

An appeals court panel ruled otherwise in February. In a 2-to-1 vote, it said the law was reasonable, a view with prominent support. In July, Chief Justice John Roberts Jr. wrote that there was “a reasonable probability” that the Supreme Court would address the issue this term in a Maryland case and that there was “a fair prospect” that it would rule as the appeals court panel had in the California case. This is a matter of national import because the federal government and more than half the states have laws allowing DNA sampling before conviction.

The constitutional outcome should be clear. Unless there is a warrant, or suspicion of a different crime that a DNA...