The Boston Police Department has pledged to make some disclosures about how they use cellphone trackers, after months of rebuffing questions on the covert surveillance technology. In a live radio interview last week, Boston Police Commissioner William Evans said his staff was gathering information to share with local civil liberties advocates.

Evans said privacy concerns about trackers were overblown and called the technology a critical tool used only under urgent circumstances. [embed][/embed] Video courtesy of WGBH. Evans went on air with WGBH’s Boston Public Radio a few hours after the New England Center for Investigation Reporting published a story on his department’s reluctance to say how it was using the trackers, also known by the common brand name, StingRays.

Evans said the tracker could be used to locate missing children, mass shooters or terrorists. “It’s basically technology that will allow us — in an emergency situation — to look at someone’s cell phone number, and if we know they’re in the area, we go to that area and we’re able to locate it,” said Evans of the technology. “It doesn’t give us any other information. All it gives us is a certain phone number.”

Evans confirmed key portions of NECIR’s reporting, including the police department’s non-disclosure agreement with the Federal Bureau of Investigation, which includes a provision that investigators would seek dismissal of criminal cases at the FBI’s request rather than divulge information about the trackers. “It’s worth dismissing a case rather than giving away the pertinent information,” said Evans, citing “national security issues” as a potential justification.

He said that police have not faced any such cases. “But that’s the agreement we signed on,” he said. “That’s how important we thought it was to get this technology.” The commissioner said the trackers are an effective public safety tool. “If we have to track down someone who’s running loose in the city — whether it’s a terrorist or a mass murderer — this is the technology we’re going to use,” Evans said.

The commissioner said that police normally seek search warrants to use the tracker, except in emergencies. He confirmed that such warrant applications don’t spell out for judges that the search would employ a cellphone tracker, specifically. Judges and civil liberties advocates in other states have criticized vague language in police requests for warrants, partly because they fear the devices will be used to snoop on holders of cellphones in the vicinity of the warrant target, whose signals they are also capable of picking up.

Evans said that his staff was currently assembling data on its tracker to share with the American Civil Liberties Union of Massachusetts, which filed a public records request with the police department in January. The state ACLU chapter is expecting information on how often Boston police have used a StingRay, the types of cases involved, and the number of warrant applications for using the device, said Jessie Rossman, a staff attorney with the ACLU of Massachusetts.

“We hope that the BPD will quickly comply with the public records law and provide these documents, as well as the warrant applications themselves, to provide much needed transparency to both judges and the general public,” Rossman said.

NECIR has a separate records request with Boston police, which was submitted last April. The police department unsuccessfully fought release of documents in two consecutive appeals to the state public records authority.