Court Upholds “Geofence” Warrant for Information on Which Phones Were Near a Crime

Starting at The Search for Information at Google; 2021WL 6111531; a decision by Magistrate Judge Michael Harvey, D.D.C.Unfortunately, I couldn’t locate a free online version of the case (it is closed on PACER). But here’s an extract:

Picture a shooting in an alley, with the footage captured on a nearby security camera. Although the video can clearly be seen, it’s too blurred to determine who committed the crime. The video clearly shows that the attacker is looking at his phone while he is walking out of the alley. The video has established the exact location of the murder. Would it then be legal for police to get a warrant using the mobile tracking capabilities of smartphones to determine who was there when the crime occurred? The Court received a warrant asking this question on October 6, 2021. However, it was not in connection with homicide cases. {The Court approved the request of the government to seal the warrant application, as the criminal investigation was not publicly available and could negatively impact the government’s investigation. This includes causing subjects to flee from or destroying evidence. Accordingly, the public version of this memorandum opinion will not disclose facts that may identify the government’s investigation or the targets of it.}

Commonly called a “geofence”, warrant by the government sought to have the Court direct Google technology to find out who crossed over into the area where criminal activity was being investigated.

Geofence warrants are a complex area of law that raises important constitutional issues. However, federal caselaw does not address their legality. The Court was able to identify four federal statutes as of the date this decision. [District Court]There were three rulings that denied the geofence warrant. The refusal to grant these warrants appears not to have affected their acceptance and use by law enforcement. A recent report shows that Google had received more than 11,554 geofence warrants by 2020, up significantly from the 982 issued in 2018. They accounted for nearly 25% of all Google warrants as of August 2021. Every warrant was approved by a judge. So, it would appear that many more geofence warrants are being granted by courts than denied….

The advent of smartphones that could track users’ locations quickly led to law enforcement seeking warrants. These warrants, also known as GPS warrants, are routine. These warrants are often authorized to allow law enforcement to trace a cell phone belonging to a suspected or known drug dealer to aid in the search for their points of sale, drug stash house, suppliers, or conspirators.

Different is the warrant in front of the Court. This warrant is known as a reverse-location warrant. The perpetrator of the crime remains unknown to law enforcement. It identifies where the criminal activity occurred and attempts to locate cell phone users who were there at the time. The “geofence” is the boundary of the area where the criminal activity occurred, and is drawn by the government using geolocation coordinates on a map attached to the warrant…. The geofence is also bound by a time window dictated by when the crime is believed to have occurred (for example, between 1:00 p.m. and 1:15 p.m. on February 15, 2021)….

Google stores location data for cell phones [from Google OS phones and other phones running Google apps] is usually quite accurate—to within 20 meters, according to Google…. Google’s location data isn’t always accurate and has a margin for error. Google states that it will accurately determine the exact location of at least 68% of its users. However, the margin of error depends on what the devices transmit. Simply put, when Google searches its servers for the devices within a defined location boundary, a device that is outside of the boundaries of the geofence may be listed as within the boundaries of the fence due to imprecision in calculating the device’s exact location….

Final piece is linking the Google user’s location data. Google gathers phone information from users when they sign up for Google accounts, according to the warrant. The registration procedure allows the user to provide Google their name, address, email, bank and other information. The account registration process is critical because many of Google’s key application and features “are accessible only to users who have signed into their Google accounts” ….

The Court won’t reveal the specifics of a criminal investigation and will instead describe only the geofence warrant application. The geofence data sought in this case covers a shipping center, where the government alleges federal crimes were committed…. To illustrate the geographic area where it seeks Google’s location data, the government has drawn a triangle on a satellite map included as an attachment to the application…. [The area of the triangle appears to be] up to 875 square meters….

For the entire geofence area, the government requests 185 minutes of information. The 185 minutes are split into segments ranging from 2 to 27 minutes on 8 specified days over a roughly five-and-a-half month period, corresponding to the criminal activity under investigation…. It can provide very specific data because the government has been able to obtain (via subpoena), CCTV footage of the shipping center that shows the criminal activity in action. The government represents that the footage shows suspects using cell phones—and in some cases more than one phone—when they engaged in that activity….

The government proposed a multi-step process for obtaining the geofence data from Google….

  1. Google can identify the devices within its range using Location History data. [geofence area]The time period laid out in [the warrant].
  2. Google will assign an anonymous identifier to each device. Google also provides the device’s coordinates, timestamps, margin of error, source(s), and sources from which it was obtained (e.g. GPS, WiFi, Bluetooth), in response to the search warrant. Google won’t provide basic subscriber information or the Google account IDs associated with devices (e.g., in this stage.
  3. This list will be reviewed by the government to determine if there are any devices that could not be related to the investigation.
  4. In addition to the Court’s legal process, the government will then need to identify all devices that appear on Google’s list.
  5. In response to this additional legal process, the Court may then order Google to disclose to the government the Google account identifier associated with the devices identified by the government to the Court, along with basic subscriber information for those accounts….

After analyzing the legal issues, the court concludes.

Because most people have their cell phones with them all the time, they can track their location and identify their location to within 20 metres. For better or worse, this feature that makes mobile devices useful to us—that gives us directions when we are lost and helps us find our phones when they go missing—leaves a digital trail behind us, the disclosure of which many would consider an invasion of privacy.

Our phones can track where we are and what time. This is a great help to law enforcement, as it allows them to pinpoint who was there when the crime occurred. This tension between legitimate law enforcement and privacy interests is what the Fourth Amendment seeks at addressing. It warrants careful consideration when considering the legality of geofence application. This is done in light of Fourth Amendment prohibition on only “unreasonable searches and seizures.”

The Fourth Amendment principles are applied here. According to probable cause, it established that there was criminal activity within the proposed geofences. Evidence related to this activity will also be found within these geofences. It has also carefully restricted the use of geofences only to the exact location and times that the crime occurred. The fact that the geofences may reveal the location information of non-suspects does not render the government’s warrant unreasonable given that the geofences and the … protocol have been crafted to minimize privacy concerns to the greatest degree possible while also preserving “the fundamental public interest in implementing the criminal law.” …