You lost some important Fourth Amendment protection when the Supreme Court ruled yesterday in Maryland v. King that the police can take a DNA sample from an arrestee without a search warrant for purposes of general law enforcement rummaging.

The court was reviewing the constitutionality of Maryland's practice of collecting DNA from all arrestees -- without a search warrant or any individualized suspicion that the DNA will lead to evidence of a crime. Maryland is not alone in this practice; 28 states and the federal government all do the same thing. Once law enforcement has a DNA sample, it's sent to a lab to extract a portion of the sample, called a DNA profile. The lab then sends that profile to an FBI-maintained database called CODIS to be compared against other profiles from genetic material left at crime scenes with the hope of solving a cold case. That's what happened to King, who was arrested for assault and, upon arrest, had his DNA collected. As the assault case worked its way through the criminal justice system, King's DNA profile ultimately linked him to an earlier, unsolved rape. King was charged and convicted of that crime and sentenced to life in prison.

There's no question that collecting DNA is a "search" under the Fourth Amendment and so ultimately the case boiled down to the purpose for which the DNA was being collected. In the past, the Court has never allowed suspicionless searches for mere investigative, crime-solving purposes because this is the key problem the Fourth Amendment was written to protect against. The Court has only allowed suspicionless searches in limited "special needs" cases where the search is for a purpose other than crime investigation, such as at a border or a sobriety checkpoint. Over the the last two years, we've argued to courts throughout the country—including filing an amicus brief with the Supreme Court in King—that warrantless DNA collection from arrestees is unconstitutional because collecting, analyzing and searching their DNA only serves a law enforcement investigative purpose to solve cold cases, and thus doesn't fall under any of the "special needs" exceptions.

Unfortunately Justice Kennedy's majority opinion didn't see it that way. In finding DNA collection from arrestees to be constitutional, the Court relied on two faulty premises.

The Court found the "search" at issue was limited to the cheek swab to obtain the DNA rather than the searches that come after, namely running the DNA sample through the CODIS database. Just like its decision last year in United States v. Jones assessing the constitutionality of installing a GPS device by looking to the law of trespass, the majority once again refused to address the privacy issues involved in searching aggregated intangible data rather than physical places or things. This has implications for other kinds of searches that don't involve physical contact and are likely to reach courts in the future, including law enforcement use of facial recognition and drones flying around in public spaces.

Then the majority found the purpose of the search was identification—ensuring the police arrested the right person—and to determine the person's prior criminal history to help a court make a correct bail determination. In doing so, the majority found collecting DNA was no different than taking an arrestee's photograph or fingerprint. But this reasoning is wrong for two reasons.

First, DNA tells far more about a person than a mere picture or fingerprint. Instead, it provides police with a person's entire genetic makeup. And even when the DNA sample is reduced to the non-coding DNA profile entered into CODIS, that profile can tell who you're related to and who you're not.

Second, in Maryland, like all other jurisdictions that collect DNA from arrestees, there's no way DNA could be used to "identify" anyone (in the ordinary definition of "identify"—which means to indicate conclusively who that person is) or to affect a bail determination from the simple fact that DNA testing takes too long and just doesn't work that way. DNA testing can't begin until after arraignment, a court proceeding when the defendant is informed of the formal charges against him and which usually takes place after his initial appearance in court, which is where bail determinations are typically made. And because of the vast amount of DNA collected by the police, coupled with the backlog in testing and the current capabilities of technology, the DNA samples sit in storage for months before they are actually tested. Finally, as Justice Scalia notes in his dissent, even once the profile is extracted, it's never compared against the offender database—only against the database of cold hits. So the real way Mr. King was "identified" was—like most other suspects today—with his fingerprint.

Justice Kennedy responds by noting "the question of how long it takes to process identifying information obtained from a valid search goes only to the efficacy of the search for its purpose of prompt identification, not the constitutionality of the search." But that misses the point. Determining the reasonableness of a search under the Fourth Amendment depends on whether the search is reasonably related in scope to the circumstances that justify the search initially. That in turn has to hinge on what the search can potentially reveal. Requiring a person to turn over their entire genome for the purpose of "identification"—a dubious proposition in and of itself—is overkill of constitutional magnitude. And by conflating "identification" with "investigation," the Court does just that.

Most troublesome, it has no limits. While the majority attempts to cabin this collection for "serious" offenses, there is no constitutional difference between a minor and serious offense. The result is that getting arrested for anything -- even driving without a seat belt -- could lead to your DNA being collected. And with studies indicating that one in three Americans will be arrested by the time they are 23, this decision will impact a a very large proportion of the American population, and, due to racial profiling endemic in policing, will once again disproporionately affect minorities.

The rise of Rapid DNA analyzers makes the problem even worse, because it makes DNA searches at station houses and in cop cars easier, regardless of whether charges are ever filed at all. The limitlesss potential of allowing this type of search goes beyond the number of people affected. When a person is arrested, should their email accounts be turned over too? How about the data on their cell phones? Surely this would help "identify" a person for bail purposes, particularly in light of Justice Kennedy's expansive definition of "identity" to cover examination of "the whole context of who the person really is."

The decision is even more troubling when you focus on the real investigative purpose of DNA collection. Of course solving crimes is a noble goal, but it bears remembering that arrestees are presumed innocent. If the mere purpose of solving crimes is enough to justify this warrantless intrusion into a person's genetic makeup, what is to stop the law enforcement from collecting DNA from everyone? Why not just collect it from babies at birth or people applying for a driver's license? 

Ultimately, in Maryland v. King, the Supreme Court effectively killed Fourth Amendment protections for the most vulnerable members of society. King's DNA could have been collected after his conviction on the assault charge, as every state and the federal government also collects DNA from convicted felons. But by authorizing warrantless DNA collection from arrestees, as Justice Scalia noted the majority managed to "to burden uniquely the sole group for whom the Fourth Amendment’s protections ought to be most jealously guarded: people who are innocent of the State’s accusations."

And while the majority hints at some limitations to the government's ability to collect DNA, the expansion of DNA collection over the last ten years (not to mention other forms of invasive evidence gathering) suggests these limitations will become meaningless without vigilant judicial supervision. The Supreme Court shrank from that responsibility with its decision and our Fourth Amendment's protections are worse off as a result.