WASHINGTON—The Central Intelligence Agency played a crucial role in helping the Justice Department develop technology that scans data from thousands of U.S. cellphones at a time, part of a secret high-tech alliance between the spy agency and domestic law enforcement, according to people familiar with the work.

The CIA and the U.S. Marshals Service, an agency of the Justice Department, developed technology to locate specific cellphones in the U.S. through an airborne device that mimics a cellphone tower, these people said.

Today, the Justice Department program, whose existence wasreported by The Wall Street Journal last year, is used to hunt criminal suspects. The same technology is used to track terror suspects and intelligence targets overseas, the people said.

The program operates specially equipped planes that fly from five U.S. cities, with a flying range covering most of the U.S. population. Planes are equipped with devices—some past versions were dubbed “dirtboxes” by law-enforcement officials—that trick cellphones into reporting their unique registration information.
The surveillance system briefly identifies large numbers of cellphones belonging to citizens unrelated to the search. The practice can also briefly interfere with the ability to make calls, these people said.

Some law-enforcement officials are concerned the aerial surveillance of cellphone signals inappropriately mixes traditional police work with the tactics and technology of overseas spy work that is constrained by fewer rules. Civil-liberties groups say the technique amounts to a digital dragnet of innocent Americans’ phones.

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The cooperation between technical experts at the CIA and the Marshals Service, which law-enforcement officials have described as a “marriage,” represents one way criminal investigators are increasingly relying on U.S. intelligence agencies for operational support and technical assistance in the wake of the Sept. 11, 2001, attacks. Many Justice Department officials view the joint effort with the CIA as having made valuable contributions to both domestic and overseas operations.

A CIA spokesman declined to comment on whether the CIA or any other agency uses the devices. Some technologies developed by the agency “have been lawfully and responsibly shared with other U.S. government agencies,” the spokesman said. “How those agencies use that technology is determined by the legal authorities that govern the operations of those individual organizations—not CIA.” He also said the relationship between the Marshals Service and CIA tech experts couldn’t be characterized as a marriage.

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A Justice Department spokesman said Marshals Service techniques are “carried out consistent with federal law, and are subject to court approval.” The agency doesn’t conduct “domestic surveillance, intelligence gathering, or any type of bulk data collection,” the spokesman said, adding that it doesn’t gather any intelligence on behalf of U.S. spy agencies.

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By DEVLIN BARRETT
Updated March 10, 2015 7:39 p.m. ET

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