Last year, the highest court in Massachusetts, the Supreme Judicial Court, issued a landmark decision in Commonwealth v. Augustine, requiring police in the state to get a search warrant before they can track individuals’ past movements using information from their cell phones. It was a significant victory for cell phone users, but unfortunately the court’s opinion also contained language that Massachusetts courts have interpreted as a loophole in the warrant requirement. Now, with help from the Berkman Center for Internet and Society at Harvard Law School, EFF and the ACLU of Massachusetts have filed an amicus brief in a new case, Commonwealth v. Estabrook, asking the high court to close that loophole.

In Augustine, following arguments made by EFF in an amicus brief in that case, the court found that under the Massachusetts state constitution, individuals have an expectation of privacy in their past movements revealed by so-called historical cell site location information (CSLI). As a result, police officers must get a warrant for CSLI, which they failed to do in obtaining two weeks of CSLI about the defendant. However, the court went on to add that it was “likely” that “there is some period of time” that was “too brief to implicate the person's reasonable privacy interest” and trigger the warrant requirement. In a footnote, the court added that “it would be reasonable to assume that a request for historical CSLI of the type at issue in this case for a period of six hours or less would not require the police to obtain a search warrant.”

That footnote from Augustine is now at play in Estabrook, although the court’s decision should be easy. In Estabrook, Massachusetts State Police once again obtained two-weeks worth of CSLI belonging to suspects in a murder without a warrant. Of course, this is an identical situation to Augustine and therefore should be held unconstitutional. However, the lower court in Estabrook refused to suppress the evidence because the prosecution attempted to exploit the potential loophole in Augustine by claiming that it was only interested in a six-hour window around the time of the murder.

As we explain in our brief, the Augustine decision settles this case. The prosecution’s argument is irrelevant because privacy intrusions occur at the time when police obtain private information, not when it is used. Augustine might be read to allow police to obtain six hours of CSLI without a warrant, but that’s not what happened here. Any other rule would totally eviscerate the warrant requirement, since police could get any amount of CSLI they wanted, then later squeak in under the wire by focusing on the most important six-hour chunk.

Although that should settle the specific issue in Estabrook, we ask the court to go further and definitively require a warrant for all CSLI. Drawing a distinction based on the duration of tracking ignores how revealing even small amounts of location data can be. In addition to its suggestion that small amounts of CSLI don’t implicate expectations of privacy, the court in Augustine may have also been motivated by a concern that police may not be able to obtain a warrant for small amounts of CSLI in some fast-moving investigations. Our brief explains that basic constitutional principles such as the “exigent circumstances” exception to warrant requirement would adequately protect public safety in these cases. In addition, clear rules benefit the public and provide guidance to police about what they can and can’t do.

Every other state to consider this issue, whether through judicial opinion or legislative action, has decided to require a warrant across the board. We hope Massachusetts will follow suit.

Many thanks to Vivek Krishnamurthy and Andy Sellars at the Berkman Cyberlaw Clinic and their students Abigail Colella, Sandra Hanian, and William Travis West for their efforts drafting the brief.