Privacy Groups Challenge Reverse Location Warrants as Unconstitutional Searches

In a filing submitted yesterday to the Ninth Circuit Court of Appeals, the Electronic Frontier Foundation and the ACLU jointly presented arguments in United States v. Spurlock, a case centered on what law enforcement calls a "tower dump" warrant. These warrants compel cellular carriers to disclose location information for every mobile device present in a specific geographic area during a particular timeframe. The case marks the first time a federal appeals court has examined such warrants following the Supreme Court's determination this summer that comparable "geofence" warrants constitute searches protected by the Fourth Amendment.

The underlying investigation involved two homicide victims found along a rural California highway, with a vehicle belonging to one victim discovered several miles away on the same stretch of road. Law enforcement obtained a tower dump warrant covering that area, which ultimately yielded location data for approximately 1,700 distinct phones. When the defendant moved to suppress this evidence, the district court applied reasoning from a Fifth Circuit decision about geofence warrants to conclude that tower dumps similarly function as unconstitutional "general warrants" under Fourth Amendment protections. Nevertheless, the court declined to suppress the evidence, invoking the "good faith doctrine."

Core Arguments in the Appeal

The privacy organizations' amicus brief presents three primary contentions regarding the constitutionality of tower dump warrants.

General Warrants and Reverse Location Searches

The brief emphasizes that the Supreme Court's ruling in Chatrie v. United States reinforces arguments that tower dumps represent unconstitutional general warrants. Though tower dumps predate geofence warrants as a surveillance method, both techniques function as "reverse location searches," enabling law enforcement to "tap into an all-encompassing database, allowing them to undertake nearly perfect, retrospective surveillance of countless persons and places." The Fourth Amendment's architects specifically sought to prevent this type of indiscriminate search. According to the filing, "Searching all people in an area without probable cause to believe they were all involved in the criminal activity under investigation reproduces the evils of general warrants and is not constitutionally permitted." This principle parallels the constitutional bar against police searching the residences of dozens or hundreds of people in a crime's vicinity.

Protective Safeguards for Innocent Parties

Even if appellate courts ultimately permit tower dump or geofence warrants in certain circumstances, the brief contends that fundamental Fourth Amendment doctrine demands robust protections for uninvolved individuals. These protections should encompass constraints on warrant scope and duration, notification requirements for affected persons, and mandatory procedures for destroying or minimizing data unrelated to the investigation.

Rejecting the Good Faith Doctrine

The organizations argue that courts must abandon the good faith doctrine in cases involving novel surveillance methods and instead directly resolve the constitutional questions at stake. The brief notes that courts frequently sidestep these determinations in cases involving emerging surveillance technologies, creating circumstances where law enforcement can employ a technique for years or decades without receiving a definitive judicial ruling on its legality.