Steps in the Geofence Process
Step One: The government first seeks anonymized numerical identifiers and time-stamped location coordinates for every device that passed through an area in a specified window of time. This information is obtained from a company, most commonly Google, using a geofence warrant. [...]
Step Two: The government reviews the list and culls it using other investigative techniques. Sometimes the government requests more information about particular accounts from the company. That request may be made by a private letter to the company for more location history for a longer period of time with no geographic limitations.
Step Three: The government further narrows the list and requests identifying information (e.g., usernames, birth dates, and other identifying information of the phones’ owners) from the company for the culled list of users through the initial warrant or an additional warrant, court order, or subpoena.