In a case with broad privacy implications, the Court of Appeals for the Third Circuit on Thursday will hear arguments on the minimum legal standards that prosecutors need to meet when requesting cell phone location data for law enforcement purposes.
The case's prosecutors have argued that to ask for data they only need to show "reasonable cause" to believe that cell phone records are relevant to an ongoing investigation. But several lower court judges and a coalition of privacy groups are arguing that authorities need to be held to the more stringent "probable cause" standard when asking for such information.
The case is important because it is the first time a federal appellate court has been asked to decide on the legal standard the government needs to use when requesting cell phone data, said Jim Dempsey, vice president for public policy at the Center for Democracy and Technology (CDT) in Washington.
The CDT has filed an amicus brief in the case. "We think the location information generated by your cell phone paints a very complete picture of your life even if you are not making a call," Dempsey said. "The premise of our argument is that cell phone tracking data is uniquely pervasive, persistent, intrusive and revealing."
Because of this, government requests for the data should require a formal warrant and not be based merely on reasonable cause, he said.
The court's ruling technically will be controlling only in the Third Circuit, and it will, to some extent, be specific to the facts of this case, Dempsey said. But the decision will have an influence on how other courts view the issue in future, he added.
The dispute stems from a 2008 request by prosecutors in Pittsburgh for cell phone location data in connection with a narcotics investigation. The request, filed under the Stored Communications Act (SCA) sought a court order requiring a cellular service provider to disclose the "transactional records" of a suspected drug trafficker.
Prosecutors wanted the service provider to include historical cellular tower data, cellular tower site information and other tracking data because they claimed there were reasonable grounds to believe the information would be relevant to its ongoing investigation.
The SCA prohibits telecommunications service providers from disclosing historical data to the government without proper legal authority. The government maintained that the reasonable cause standard was all that was required to obtain that legal authority.
However, the Pittsburgh magistrate judge to whom the request was made denied the government's request and held that cell phone tracking data was protected under the provisions of the Fourth Amendment.
In a 52-page ruling, the judge maintained that prosecutors needed to obtain a formal warrant showing probable cause to believe that the information being sought would be useful as evidence in a criminal investigation.
Cell phone location information "is not "voluntarily and knowingly" conveyed by cell phone users," magistrate judge Lisa Lenihan wrote. Unlike dialed telephone numbers, location information is automatically registered by the cell phone, with no action on the part of the user, and it can reveal a lot of information about the user, the judge said.
Cell phone location information is "extraordinarily personal and potentially sensitive" the judge wrote. While "law enforcement's investigative intrusions on our private lives, in the interests of social order and safety, should not be unduly hindered," it must be balanced by appropriate degrees of accountability, she said.
In an unusual move, the judge decided to make her opinion public -- though none of the parties in the government request were named. The magistrate judge's decision was signed by four other judges in the Western District of Pennsylvania and later affirmed by a U.S. District Court judge as well.
In its appeal, the government argued that no Fourth Amendment rights were being implicated by its request, and it said that the SCA allowed the government to obtain location information from providers based on reasonable cause. The government has contended that there can be no reasonable expectation of privacy in cell phone location data, just as there isn't with data about dialed numbers.
Dempsey said that almost all government requests for cell phone tracking data to date have been handled by magistrate judges. "Over the past five years, magistrate judges have been taking a closer look and turning down a lot of the government's requests," he said.
In all the other cases, the government has chosen not to appeal, he said. In this case, the fact that all other magistrate judges in the Western District of Pennsylvania took the same position may have pushed the government appeal, he said.
A decision in the case could take months.
Jaikumar Vijayan covers data security and privacy issues, financial services security and e-voting for Computerworld. Follow Jaikumar on Twitter at @jaivijayan or subscribe to Jaikumar's RSS feed . His e-mail address is jvijayan@computerworld.com.