Federal investigators in Northern California routinely used a sophisticated surveillance system to scoop up data from cellphones and other wireless devices in an effort to track criminal suspects — but failed to detail the practice to judges authorizing the probes.
The practice was disclosed Wednesday in documents obtained under the Freedom of Information Act by the American Civil Liberties Union of Northern California — in a glimpse into a technology that federal agents rarely discuss publicly.
The investigations used a device known as a StingRay, which simulates a cellphone tower and enables agents to collect the serial numbers of individual cellphones and then locate them. Although law enforcement officials can employ StingRays and similar devices to locate suspects, privacy groups and some judges have raised concerns that the technology is so invasive — in some cases effectively penetrating the walls of homes — that its use should require a warrant.
The issues, judges and activists say, are twofold: whether federal agents are informing courts when seeking permission to monitor suspects, and whether they are providing enough evidence to justify the use of a tool that sweeps up data not only from a suspect’s wireless device but also from those of bystanders in the vicinity.
In Northern California, according to the newly disclosed documents, judges expressed concerns about the invasive nature of the technology.
“It has recently come to my attention that many agents are still using [StingRay] technology in the field although the [surveillance] application does not make that explicit,” Miranda Kane, then chief of the criminal division of the Northern California U.S. attorney’s office, said in a May 2011 e-mail obtained by the ACLU.
As a result of that, she wrote, “effective immediately, all . . . applications and proposed orders must be reviewed by your line supervisor before they are submitted to a magistrate judge.”
The Justice Department has generally maintained that a warrant based on probable cause is not needed to use a “cell-site simulator” because the government is not employing them to intercept conversations, former officials said. But some judges around the country have disagreed and have insisted investigators first obtain a warrant.
“It’s unsettled territory,” said one U.S. law enforcement official, who spoke on the condition of anonymity because he was not authorized to speak for the record.
