Deeplinks
This blog post was drafted with help from former EFF Legal Intern Emma Hagemann.
Massachusetts’ highest court has upheld the collection of mass cell tower data, despite recognizing that this data not only provides investigators with “highly personal and private” information but also has the potential to reveal “the locations, identities, and associations of tens of thousands of individuals.”
The case is Commonwealth v. Perry, and in it the Massachusetts Supreme Judicial Court (SJC) addressed the constitutionality of “tower dumps” of cell site location information (CSLI).
A “tower dump” occurs when a phone company provides law enforcement with data on all devices that connected with a specific cell tower during a specified period of time. Because each cell tower covers a particular geographic area, police can infer from the data that the device owners were in that area at the time. Tower dumps can identify hundreds or thousands of phones—or, in this case, “more than 50,000 individuals . . . without any one of them ever knowing that he or she was the target of police surveillance.”
In Perry, after a series of six store robberies and one homicide, law enforcement sought and obtained two tower dump warrants. Together, the warrants covered seven cell towers on seven different days over the course of a month. Officers cross-referenced the tens of thousands of phone numbers they obtained to identify devices that pinged multiple towers on the days the crimes occurred. Through this process, they were able to identify Mr. Perry as a suspect. Mr. Perry moved to suppress the evidence.
EFF, along with ACLU and the Massachusetts Committee for Public Counsel Services, filed an amicus brief in the case, arguing that a tower dump is a general search that violates the Fourth Amendment and Article 14, Massachusetts’ constitutional equivalent. Like the general warrants reviled by the Constitution’s drafters, tower dumps are irremediably overbroad because they sweep up the information of hundreds or thousands of people that have no connection to the c
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