When it comes to searching the most sensitive part of our bodies—our DNA—the Fourth Amendment's prohibition against unreasonable searches and seizures should be a strong bulwark, keeping the government out of our most personal and private biological information. But in the last few years, those protections have been eroded as courts throughout the country, including the US Supreme Court, have approved of the warrantless DNA collection of people arrested for crimes—individuals who are presumed to be innocent in the eyes of the law. A new amicus brief we filed on Monday argues that these decisions don't mean the complete death of Fourth Amendment protection from DNA collection.

This summer, the Supreme Court issued its disappointing decision in Maryland v. King, approving Maryland's warrantless DNA collection scheme from pretrial arrestees. The court reasoned that the purpose of collecting DNA is "identification," or to make sure the police had arrested the right person, noting that collecting DNA was similar to the routine police practice of collecting a fingerprint.

Following the Supreme Court ruling, the Ninth Circuit Court of Appeals asked for amicus briefs to address what impact King would have on the court's review of Haskell v. Harris a case in which the ACLU of Northern California is challenging Proposition 69, a warrantless DNA collection program approved by California voters in 2004. We filed a new amicus brief, explaining that even after King, Prop 69 is unconstitutional. It's the second amicus brief we've filed in this important privacy case.

Our new brief explains that although King approved of Maryland's DNA collection scheme, it didn't approve all warrantless DNA collection schemes per se. Instead, the Supreme Court has consistently said that what is "reasonable" under the Fourth Amendment depends on the "context" in which a search takes place and so the Ninth Circuit would have to look at California's law anew.

While King focused on "identification" and equated DNA with a fingerprint, we explain how DNA reveals far more information than a mere fingerprint, since DNA contains our entire genetic makeup, revealing where we came from, who we're related to and whether we're likely to get certain diseases. Nor does the government need DNA to "identify" the person they've arrested since fingerprints have proven to be a effective way to ensure the police have the right person without implicating the same privacy concerns as DNA collection. As the government's ability to collect DNA rapidly expands, the court must impose some limits to prevent the real harms that occur with excessive DNA collection, including false identification of innocent people.

DNA collection is just another example of the government's use of technology to shrink privacy and push the boundaries of what it can collect outside the confides of the Fourth Amendment. We hope the Ninth Circuit will appreciate that Maryland's collection scheme is different than California's and find Prop 69 unconstitutional.

The Ninth Circuit will hear oral argument in Haskell sometime in December in San Francisco.