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, part of a little-known high-tech alliance between the spy agency and domestic law enforcement, The Wall Street Journal reported, quoting unnamed sources.

Together, 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 was first reported by The Wall Street Journal last year, is used to hunt criminal suspects. The same technology is used to hunt terror suspects and intelligence targets overseas, the people said in the article published Tuesday.

The Justice Department 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 as ?dirtboxes? by law-enforcement officials?which trick cellphones into reporting their unique registration information. In that way, 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, however, are concerned the aerial surveillance of cellphone signals inappropriately mixes together 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.

The CIA has a long-standing prohibition that bars it from conducting most types of domestic operations, and officials at both the CIA and the Justice Department said they didn?t violate those rules.

The cooperation between the CIA and the Justice Department on this technology began a decade ago, when the spy agency arranged for the Marshals Service to receive more than $1 million in gear to conduct such surveillance, said people familiar with the program. In total, more than $100 million went into research and development of the devices.

For years, the U.S. Marshals? Technical Operations Group worked with the CIA?s Office of Technical Collection to develop the technology. In the early days it was the CIA that provided the most resources, said the people familiar with the matter.

The CIA gave the Marshals Service the ability to conduct what officials called ?silent stimulation? of cellphones. By using a device that mimics a cell tower, all phones in range of that tower send in their identifying information. When the device finds the target phone it is seeking in that sea of information, the plane circles over the phone until the device can locate it to within about 3 yards.

Some versions of the technology can do more than just identify and locate the phone. They can also be used to intercept signals coming from the phone, these people said. U.S. military and intelligence agencies have used the technology in Afghanistan, Iraq, and elsewhere to hunt terrorists, and map the use of cellphones in such places, according to people familiar with the work.

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, terror attacks. Within the Justice Department, many officials support 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 the CIA?s tech experts couldn?t be characterized as a marriage.

The Justice Department, which oversees the Marshals Service, would neither confirm nor deny the existence of such technology, saying that doing so would tip off criminals. A Justice Department spokesman said Marshal Service?s 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 the agency also doesn?t gather any intelligence on behalf of U.S. spy agencies.