It just got a bit harder for law enforcement agencies to turn your cell phone into a personal homing beacon: A federal court has slapped down the Justice Department's appeal of a February ruling that required investigators to seek a probable cause warrant before acquiring historical records of a cell phone users physical movements.
In a curt opinion released late Wednesday, Judge Terrence McVerry of the United States District Court for the Western District of Pennsylvania affirmed that February's decision by Magistrate Judge Lucy P. Lenihan, writing for a unanimous five-judge panel, was "not clearly erroneous or contrary to law." The Justice Department had asked the court to overturn Lenihan's order, while an amicus brief filed by the Electronic Frontier Foundation, American Civil Liberties Union, and Center for Democracy and Technology had urged McVerry to ratify the lower court's holding that a showing of probable cause was needed before a cell provider could be compelled to disclose geographic data about a subscriber.
The central point of contention between the government and civil liberties groups concerned whether records revealing the nearest cell tower to a subscriber's phone at the time of a call—information sufficient to pinpoint the phone's location only within several hundred feet—could be obtained using a "D order" based on "specific and articulable facts" showing its relevance to an ongoing investigation. This intermediate evidentiary standard is greater than what would be required to subpoena records, but less stringent than the "probable cause" required for a Fourth Amendment warrant.
Interestingly, both the government and civil liberties groups agreed that the lower court had erred in resolving the question by reference to language in the Communications Assistance for Law Enforcement Act pertaining to "tracking devices." (The appeals court declined to revisit this point.) Both the civil libertarians' amicus and the government's reply memorandum argued that the controlling statute was the Stored Communications Act, governing records pertaining to subscribers. That act permits judges to issue "D orders" for records on the basis of "specific an articulable facts," but the civil liberties groups argued that this establishes a "floor" rather than a "ceiling," leaving the courts leeway to impose a higher standard when disclosure of records might implicate Fourth Amendment interests.
The government cited precedent suggesting that the use of tracking technology did not amount to a Fourth Amendment search when it disclosed no more than could be gleaned from physical surveillance of a target in public places—as when a tracking beacon is attached to an automobile on public highways. Because cell tower data provides only a very approximate location, they contended, it did not permit the sort of detailed tracking that would permit authorities to follow targets' movements in protected private spaces. Moreover, Justice Department attorneys argued, the Supreme Court has ruled that information voluntarily disclosed to third parties—as when customers provide the phone company with a dialed number—falls outside the ambit of the Fourth Amendment. Therefore, according to the government, the court should refrain from imposing a standard higher than specified by statute.
The court, however, appears to have been more persuaded by EFF and amici, who distinguished cell location data from automobile beacons, noting that it would permit law enforcement agencies to make inferences about the movements of persons—as well as about who was in possession of the phone at any given time—whether in public or private spaces. Moreover, they argued, a lax standard for seeking location data "enables dragnet surveillance" by permitting the government to acquire location records in bulk, then hunt for a particular pattern of movements. Though amici conceded that the government hadn't attempted such dragnet surveillance in the instant case, they warned that cell phone tracking nis "ripe for such use."
Justice Department spokesman Dean Boyd told Ars that the government is reviewing the court's decision, but could not say whether an appeal is planned.Posted on