The use of a new investigative technique by law enforcement, called a geofence warrant, has been gradually emerging over the past year. Google is at the forefront of the early media attention and the nascent legal developments in the United States. Two federal magistrate judges in three separate opinions in the United States District Court for the Northern District of Illinois in Chicago recently ruled that a geofence warrant violates the Fourth Amendment requirements of probable cause and particularity.

1. Introduction

In a post to Lawfare earlier this year titled Do Geofence Warrants Violate the Fourth Amendment? dated February 24, 2020, Nathaniel Sobel described a geofence warrant as distinct from traditional warrants in that it permits law enforcement to work backwards. “These warrants,” he said, “compel a technology company (so far, only Google) to disclose anonymized location records for any devices in a certain area during a specified time period.” Following the seizure of location records, the government “may obtain additional location data and subscriber information.” (here) Google has reported a 1,500% increase in the number of geofence requests it received in 2018 compared to 2017. As of December 2019 the rate increased over 500% from 2018 to 2019. A geofence warrant, then, authorizes the search of everyone in order to identify someone.

2. The Illinois Litigation

The police were investigating the suspected theft of pharmaceuticals and had evidence that an unknown subject entered two physical locations to receive and ship stolen medication at specific times. The government wanted to know which mobile or smartphone devices, that transmitted location information to Google, could be known by Google to have been at those two locations at the times when the unknown subject was there. In a ruling reported as In re Search of Information Stored at Premises Controlled by Google dated August 24, 2020, Magistrate Judge Gabriel Fuentes described the idea behind a geofence warrant, at p. 1, as casting a “virtual net” around a particular location for a particular time frame. The government sought to erect three geofences; two at the same location for different time frames and one at a second location. The ruling has also been reviewed and linked to a post by Jennifer Lynch and Nathaniel Sobel to the Electronic Frontier Foundation’s website titled New Federal Court Rulings Find Geofence Warrants Unconstitutional dated August 31, 2020. (here)

The application before Judge Fuentes was the third application by the government during the same investigation. The first application was denied by Magistrate Judge David Weisman reported as In re Search of Information Stored at Premises Controlled by Google dated July 8, 2020. The second application filed on July 24, 2020, narrowed the geographical scope of the three proposed geofences “drawing them more tightly around the two physical locations where the Unknown Suspect was seen entering to receive or ship the stolen medication, and attempting to reduce the number of devices (and persons) identified in the search.” Judge Fuentes denied the second application on July 24, 2020, relying on the previous ruling by Judge Weisman that “the warrant failed to meet the Fourth Amendment’s particularity requirement and failed to establish probable cause to seize the location information of device users […] who could not be shown to be involved in the subject offense.” I will limit my comments to the third ruling as it is the more extensive one and may be of more interest.

3. The Third (Amended) Application

In the third application, the geographical scope of the geofences was unchanged from the second application that was denied by Judge Fuentes on July 24, 2020. However, the government altered the proposed search protocol to eliminate the third of three stages that were proposed in the first two applications. The three stages were: (1) Google’s collection of information it possessed about devices it believed traversed the geofences; (2) Google’s production of an “anonymized” list of the unique device IDs for those devices as well as related information including their location coordinates and time stamps; and, (3) Google’s production of the subscriber information identifying the account holders or users of the devices on the anonymized list, with the government exercising its discretion as to the device IDs for which Google would obtain identifying subscriber information and provide it to the government.

With the elimination of the third stage, the government argued that the constitutional infirmities identified in the two previous rulings had been cured because the proposed warrant did not seek “any individual identifying information” and could not be used “to identify a device’s user without further information from Google.” The two locations targeted by the proposed warrant included: (a) an area around a commercial enterprise located in a mixed-use commercial and residential building located in a busy area on a major arterial street; and, (b) a commercial area and parking lot that operated as a stand-alone building where there were no other apparent business or residential users. Let’s turn, then, to Judge Fuentes’ treatment of the probable cause and particularity requirements of the Fourth Amendment.

(a) Probable Cause

The government argued that a geofence warrant is akin to a “tower dump” in which cell site location information for multiple persons not known at the outset of the search is disclosed “based on such persons’ devices having been near or in contact with particular cell towers.” That argument was rejected where Judge Fuentes held, at p. 31, that the government did not establish probable cause to believe that “evidence of a crime will be found in the location history and identifying subscriber information of persons other than the Unknown Subject.” It was likely that the warrant would generate information, not only about the unidentified subject, but also about persons not involved in the crime being investigated. The asserted probable cause for the search therefore resembled the argument that “probable cause exist[ed] because those users were found in the place to be searched, i.e., the place as to which probable cause exists to believe the offense happened.”

That kind of warrant, known as an “all persons” warrant, was rejected by the United States Supreme Court in Ybarra v. Illinois, 444 US 85, 91 (1979) where the police obtained a warrant to search a public tavern and the bartender for narcotics but also searched a bar patron: “[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.” (here) Judge Fuentes therefore concluded, at p. 33, that “[n]o such predicate [was] established here.” He went on, at p. 35, to hold that there must be “at least some evidence of a person’s involvement in the suspected crime” to allow a search of location information “in which the person has a constitutionally protected expectation of privacy.” (See also: Marks v. Clarke, 102 F.3d 1012, 1029 (9th Cir. 1996) and Owens ex del. Owens v Lott, 372 F.3d 267, 276 (4th Cir. 2004)

(b) Particularity

The Ybarra court also relied on the particularity requirement in the Fourth Amendment, and the prohibition against general warrants, at p. 92 n. 4, to find that “a warrant to search a place cannot normally be construed to authorize a search of each individual in that place.” The proposed geofence warrant was therefore over-broad and not saved by being “narrowly tailored” on the third application. The geofence warrant was distinguishable from the warrant that authorized deployment of a cell site simulator in U.S. v. Sanchez-Jara, 889 F.3d 418, 421 (7th Cir. 2018) “to identify two specific phones and to follow those phones and determine the user’s physical location or movements.” The warrant upheld in Sanchez-Jara met the particularity requirement because it specified the devices to be identified. (here) However, as Judge Fuentes held, at p. 38, the proposed geofence warrant in the amended application “[did] not come close to doing so.”

Judge Fuentes continued, at p. 38, to emphasize that the proposed geofence warrant left to the executing police officer’s discretion the identifying information that was to be obtained based on the review of the devices IDs and time stamps to determine which devices might belong to the unknown subject but also those who might be a witness to the offence. The geofence warrant was therefore unlike the warrant for the cell site simulator in Sanchez-Jara “which suggests” that a warrant that does not identify the target device fails the Fourth Amendment test. “The amount of discretion,” Judge Fuentes concluded at p. 40, “[was] too great to comply with the particularity requirement”.

4. Conclusion

The United States Supreme Court has recognized the ubiquity of mobile electronic devices in modern life and the privacy interests inherent in their use – including location data. As Judge Fuentes said, at p. 41, technological advances must not diminish Fourth Amendment protections that are rooted “in the reviled abuses of colonial times.” However, he emphasized that, although the application in this case did not clear Fourth Amendment hurdles, that does not “suggest that geofence warrants are categorically unconstitutional.” (See: Carpenter v. U.S. and Riley v. California that I discussed in previous posts to On The Wire here and here)

Mr. Sobel suggested in his post to Lawfare, where he commented on the briefings from the defence, the government and Google’s amicus brief filed on the motion to suppress in U.S. v. Chatrie, that the ultimate resolution of the constitutional issues raised by geofence warrants is “enormously consequential” for the scope of Fourth Amendment protections in the digital age. But it will be a resolution years in the making. The rulings on the Illinois applications are decisions at the trial level. The courts in the United States are just beginning to “grapple with the challenge of applying Carpenter in contexts outside of a warrant for a single person’s cell phone location data.”