The use by U.S. investigators of a sophisticated device known as a StingRay, which simulates a cellphone tower and enables agents to locate and monitor individual cellphones, was revealed Wednesday in documents obtained under the Freedom of Information Act by the American Civil Liberties Union of Northern California, The Washington Post reported.
Privacy groups and some judges suggested the use of the technology, which is so sensitive it can penetrate the walls of homes, shouldn't be allowed without a warrant.
They question whether federal agents are providing sufficient evidence to judges to justify the use of a tool that captures data not only from a suspect's wireless device but also from those of bystanders in the vicinity.
Some judges in Northern California have expressed misgivings about the use of the StingRay 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, former chief of the criminal division of the Northern California U.S. attorney's office, said in May 2011 email obtained by the ACLU.
Some judges around the United States have begun to insist investigators first obtain a warrant before deploying the technology.
"By withholding information about this technology from courts in applications for electronic surveillance orders, the federal government is essentially seeking to write its own search warrants," Linda Lye, a staff attorney for the ACLU of Northern California, told the Post.