United States v. Gilton (Amicus Brief)

The U.S. Court of Appeals for the Ninth Circuit will hear an interlocutory appeal about whether access to historical cell site location information (CSLI) requires a warrant under the Fourth Amendment. The Brennan Center – in conjunction with Electronic Frontier Foundation, Center for Democracy and Technology, American Civil Liberties Union, American Civil Liberties Union of Northern California, and National Association of Criminal Defense Lawyers – has filed an amicus brief in support of a warrant requirement.

Cell site location information is generated and logged each time a phone connects to a cell tower to send or receive data. Cell service providers are able to store information about which tower (or towers) the phone connected to for any given call, text, email, or similar data request for up to five years. Most Americans carry their phones with them everywhere they go, and the rise of smart phones in recent years has resulted in a massive increase in the frequency of data transmission. Consequently, aggregated CSLI can produce a much more detailed account of an individual’s movements than visual surveillance or GPS tracking on an individual’s car. Law enforcement agencies now request this data from service providers tens of thousands of times per year. Yet there is no consensus in appellate or federal courts as to whether or not access to this data requires a warrant under the Fourth Amendment.

In United States v. Gilton, the district court ruled that the Fourth Amendment demands police get a warrant. In the course of investigating a homicide, the San Francisco Police Department applied for and obtained search warrants for the historical CSLI of suspects Antonio and Barry Gilton. Gilton moved to suppress the CSLI data on the grounds that the warrant affidavit did not provide substantial basis for concluding that there was probable cause to search his phone records. The district court held that: (1) historical CSLI records are subject to Fourth Amendment protections, and therefore require a warrant for search; (2) the warrant lacked probable cause as to Antonio and was therefore invalid; and (3) the good-faith exception to the warrant requirement does not apply in this circumstance because the warrant was so obviously lacking in probable cause that no reasonable officer could have relied on it in good faith. The government filed for interlocutory appeal to the Ninth Circuit.

The Brennan Center’s amicus brief argues that CSLI deserves Fourth Amendment protections because it reveals private, invasive, and increasingly precise information about individual’s locations and movements. Unlike visual surveillance, it enables law enforcement to reconstruct a person’s movements well after the fact, including in and around constitutionally protected spaces, at minimal expense, in defiance of societal expectations. Lastly, it argues that the “third party doctrine” – a legal principle holding that in most cases, information shared with a third party (such as a cell service provider) is not entitled to a reasonable expectation of privacy – should not apply to CSLI due to the sensitivity of the information, the involuntary and often unconscious nature of the transmission, and the lack of meaningful alternatives to generating and sharing this type of data with a third party (outside of not using a phone). The brief urges the Ninth Circuit to uphold the district court’s ruling and recognize that CSLI is so sensitive that the Fourth Amendment requires a warrant for police to access it.

Read the brief here.