This week, the Supreme Court considered whether collecting DNA from an arrestee was an unreasonable Fourth Amendment search.

Or at least that would have been a good way for the Court to frame the question.

Instead, much of the oral argument in Maryland v. King dealt with the question whether swabbing the cheek of an arrestee to take a DNA sample upsets one’s reasonable expectations of privacy. The “reasonable expectation of privacy” test is doctrine that arose from Justice Harlan’s concurrence in Katz v. United States. The test asks whether a person claiming the Fourth Amendment’s protections had a subjective expectation of privacy and whether it is “one that society is prepared to recognize as ‘reasonable.’ ”

The government’s case rests on that framing, which is why Deputy Solicitor General Michael Dreeben began his argument by saying that arrestees are “on the gateway into the criminal justice system. They are no longer like free citizens who are wandering around on the streets retaining full impact Fourth Amendment rights. The arrest itself substantially reduces the individual’s expectation of privacy.”

It’s true that an arrestee has his privacy and other liberties invaded various ways. What problem is it if a bit of DNA is collected at the same time? It’s pretty much like finger printing, the argument goes…

The “reasonable expectation” test is almost never faithfully followed by courts. My guess is that the Court will not assess whether King himself actually expected “privacy.” That would encompass everything from believing that none of his mucus membranes would be collected by a government agent, to believing that his genetic material would neither be analyzed nor preserved in a Maryland lab for further analysis somewhere in an uncertain future.

When it applies the objective part of the test, there is a chance, but I’ll be surprised if any justice actually examines the difference in experience between fingerprinting and DNA collection, such as by comparing the slim privacy invasion when one person touches another’s hands to the real invasion that occurs when a person puts something in another person’s mouth. Doing so in its exercise of free-form interest balancing could, but probably wouldn’t, overcome the government’s interest in using “the fingerprinting of the 21st Century” to catch crooks.

Rather than using doctrine and making policy judgments, the Court should assess the government’s actions as the Fourth Amendment commands. The law does not invite the Court to examinine what people may or may not think about “privacy.” It bars the government from committing unreasonable searches and seizures.

If one examines the case guided by the words of the Fourth Amendment, what happened is far more clear. Taking a bodily specimen from Alonzo King was, in natural language, a seizure. Processing that specimen to create an identity profile was a further examination, bringing otherwise concealed information into law enforcement’s view. And comparing King’s identity profile to cold-case profiles was incontrovertibly looking for something. This is all searching using that seized bodily material.

Now, was the search reasonable?

Having been picked up on a variety of assault charges, King’s mouth was swabbed and his DNA taken, processed, and used to investigate whether genetic material matching his was associated with any other cases. It’s the equivalent of taking keys on the person of an arrestee and looking through his house for evidence of other crimes. There was no relationship between King’s alleged wrongdoing and the investigation conducted using his DNA.

Perhaps it is reasonable to conduct a free-form search into the biography of a person who has been arrested–that is, a person about which a law enforcement officer says he has probable cause to arrest–but it is unlikely. The Fourth Amendment’s particularity requirement suggests that it is unreasonable to investigate a person arrested for one crime to see what other, unrelated crimes he may have committed.

Counsel for the State of Maryland rested her argument heavily on the use of information about other crimes in bail decisions. This falls apart under the same logic, unless the Court is going to produce a rule that the Fourth Amendment allows the government carte blanche to search and seize when a bail hearing is pending. And the DNA results came back months after Alonzo King’s arraignment.