Privacy After Carpenter v. United States: Can a Tower Dump Warrant Meet the Warrant Requirement?

• Author: Bramley-Garoutte, Sarah

"[A] person's mere propinquity to others independently suspected of criminal activity does not, without more, give rise to probable cause to search that person." (1)

1. Introduction

   Cell phone users create a detailed, time-stamped record of their movements everywhere they carry their phone. (2) Cell site location information (CSLI) refers to this record that cell phones send to the user's service provider (provider). (3) Beyond turning the cell phone off or disconnecting it from the cellular network, there is no way for users to avoid creating CSLI. (4) Consequently, the vast majority of adults in America are sending mass amounts of location data to their providers. (5) Providers store CSLI along with personal identifiable information (PII) about cell phone users. (6) Yet providers are not the only ones with access to this information--providers often grant access of CSLI and PII to law enforcement for criminal investigations. (7) Government officials, including law enforcement and prosecutors, can even request the CSLI and PII of all users who connected to cell sites in a certain area during a specified time--including those who have not even been suspected of a crime--which is termed a cell tower dump. (8)

   Technological advances like CSLI have implicated the general public's privacy concerns, but the Supreme Court has continually iterated its support for preserving the degree of privacy that existed at the time of the Fourth Amendment's adoption. (9) This support has not been without great exception, however, as the Court previously established in the third-party doctrine that one does not have a legitimate expectation of privacy in information they voluntarily share with third parties. (10) In Carpenter v. United States, the Supreme Court readdressed the third-party doctrine in answering whether the Fourth Amendment protects historical CSLI--seven days or more of a user's CSLI. (11) In this landmark decision, the Court declined to extend the third-party doctrine to CSLI because of CSLI's unique nature. (12) The Court noted CSLI is inescapable tracking that follows every cell phone user. (13)

   The Court's narrow holding in Carpenter clarified the protection afforded to historical CSLI but left tower dump and real-time CSLI unprotected. (14) As such, Carpenter has left lower courts to grapple with the distinction between tower dump CSLI, which can implicate thousands of user's location information, and the historical CSLI of one user; particularly, whether their differences warrant different treatment under the Fourth Amendment. (15) Perhaps due to the ongoing uncertainty, some states have enacted legislation requiring law enforcement to obtain a warrant for any CSLI--effectively prohibiting the government from conducting a warrantless tower dump. (16)

   This Note examines the tension between the warrant requirements and a typical tower dump warrant that names no person or suspected phone number. (17) After detailing Fourth Amendment jurisprudence, Part II outlines CSLI jurisprudence. (18) Part III then compares a tower dump warrant to an "all-person" warrant prohibited under the Fourth Amendment while analyzing the warrant requirements. (19) This Note concludes by proposing how courts should limit law enforcement's use of tower dumps to comply with constitutional warrant requirements. (20)

2. HISTORY

   1. CSLI

      For cell phones to serve their intended purpose of providing a communication medium, they must send and receive data by wirelessly connecting to a cellular network through cell sites--antennas affixed to the company's cell towers or other tall structures. (21) Each cell tower generally has numerous cell sites facing different directions, and each cell site contains multiple antennas that allow cell phones to connect to the network. (22) As a user moves away from one cell tower and closer to another, their cell phone automatically transfers its connection to the strongest cell site. (23) Cell phones connect to cell sites both periodically while the cell phone is on and whenever the user initiates a function requiring a cellular connection. (24) While not every function on a cell phone requires a cellular connection, a cell phone must be able to connect to the network to send a text, make a call, use an application, or complete any other function which requires cellular connection. (25) Consequently, cell site connections may occur every few minutes, but can be as frequent as every seven seconds. (26)

      For every cell site connection, cell phones generate and send location information to the user's provider that the provider then stores. (27) Providers typically retain CSLI for at least a year, but some large providers retain it indefinitely. (28) CSLI usually includes the date of the connection, start and end time of the connection, and the location of the connection. (29) Additionally, CSLI includes the user's phone number or unique identifier number so providers can identify which user connected to the network through that cell site. (30) Providers further maintain extensive records of PII, including an individual's name, address, call records, date of birth, social security number, driver's license number, and banking information. (31)

      CSLI shows a cell phone's location and movements, both in the past and in real time. (32) Historical CSLI refers to the record of a user's past location data that law enforcement can request after the fact. (33) Real-time CSLI refers to location data of a user's movements as they occur. (34) Law enforcement can obtain realtime CSLI by requesting the provider "ping" the cell phone, which forces the cell phone to reveal its current location by connecting to the nearest cell site. (35)

      The accuracy of CSLI depends upon the number of cell sites near the cell phone. (36) More cell sites mean smaller coverage areas, leading to cell phones transmitting more precise location data to providers. (37) While varying cell site numbers means the accuracy of a user's location will depend on the area traveled, CSLI can usually show the user's location down to a few hundred feet or less. (38) As technology has advanced, the precision of CSLI has increased and has approached that of GPS. (39) Providers are also installing more cell sites to handle the growing data usage by more users, leading to ever smaller coverage areas. (40) Some cell sites even employ newer, more advanced technology that allows CSLI to place a user down to the floor of a building. (41)

   2. Tower Dump

      When law enforcement submits a tower dump request, providers generate a report of CSLI for all users that connected to a cell site within the specified location and time range. (42) This report generally includes the user's cell phone number and CSLI--a record of the date, start and end time, the location, and tower side of the cell site connection. (43) Additionally, because providers collect extensive amounts of PII, law enforcement can request providers also disclose the desired PII of ensnared users. (44) Although providers are required by law to maintain and protect CSLI and PII, they receive frequent requests for this data from law enforcement and will disclose it if law enforcement has complied with applicable law and policy. (45) While courts disagree as to whether PII is disclosed alongside CSLI in a tower dump report, law enforcement may choose to originally request disclosure of both, and providers will usually comply. (46) As noted by the Supreme Court, the gathering of CSLI from providers is cheap, easy, and efficient when compared to traditional investigative techniques. (47)

      Under the Stored Communications Act (SCA), law enforcement has warrantlessly requested CSLI from providers for over a decade. (48) Providers have faced an increasing number of requests for CSLI in recent years, including for tower dumps. (49) As providers retain CSLI records, law enforcement is able to request a cell phone user's recent and historical movements, spanning back years. (50) A tower dump, however, does not just reveal a single user's movements: A tower dump report can reveal thousands--even hundreds of thousands--of users' movements. (51)

      The use of a tower dump is well-suited for investigating serial crimes: Law enforcement can cross-reference phone numbers across each crime scene under the assumption an innocent individual is unlikely to be present for multiple crimes. (52) After receiving multiple tower dump reports corresponding to the time and location of the crimes, law enforcement can compare the phone numbers from the reports to narrow down on a suspect device present across numerous scenes. (53) Scholars recognize that a tower dump can also be helpful where law enforcement has identified the crime scene location and timeframe but has not identified the suspect, although the use of a tower dump for identification rests upon the assumption that the suspect carried their cell phone with them. (54) A tower dump, however, yields innocent users alongside guilty users, so its use for criminal investigations may be limited. (55)

      A tower dump is distinct from the more precise location information that Google stores, which law enforcement seek through geofence warrants. (56) Google stores location information that is considerably more accurate than CSLI, information gathered through user-enabled features on the cell phone, such as GPS, Wi-Fi, and Bluetooth. (57) Signals from GPS, nearby Wi-Fi networks, and Bluetooth devices provide additional location information and allow for greater precision in estimating the cell phone's location. (58) In contrast, CSLI relies on location information from cell sites alone. (59) Additionally, many cell phone users actively enable such location tracking by Google, whereas cell phone users are not given the option with CSLI. (60)

   3. Fourth Amendment Jurisprudence

      1. Searches

         The Fourth Amendment protects individuals' privacy from unreasonable governmental intrusion. (61) To trigger...