Dozens of police departments nationwide are using cell phone tracking technology, otherwise intended for federal agencies to hunt terrorism suspects, to pursue a range of crimes in their jurisdictions, from the most serious to the most petty, a recent investigation by USA Today found.

But in cases where the technology was used to track a suspect via cell phone triangulation, departments rarely, if ever, disclose their methodology, thanks to non-disclosure stipulations between departments, federal agencies, and private manufacturers from which the technology is purchased. Police in some cities have used the technology with surprising regularity, the investigation found, but experts worry that prevailing secrecy has led to troubling omissions in public accountability and court proceedings where defense attorneys and judges have not been privy to the knowledge that electronic surveillance was used and therefore unable to assess the method's legality.

If police departments do not first obtain court authorization to collect evidence using the technology, judges can suppress that evidence and dismiss the case. Prosecutors, thanks to non-disclosure agreements, are given top-down recommendations to drop cases if the details of the technology risk being exposed. But according to the American Civil Liberties Union (ACLU), many defense attorneys are not aware when the technology is used.

"This is entirely understandable because the federal government... appears to be providing misleading information and making material omissions to judicial officers when it seeks purported court authorization to use this device," reads an ACLU guide for defense lawyers. 

The use of such technology by local departments has been well documented, but the investigation paints a broader picture of what that use looks like.

Much like with the civil liberties concerns raised over the bulk data collection by the National Security Agency following revelations made by former security contractor Edward Snowden in 2013, observers worry about the implications of departments' indiscriminate collection of cell phone data via technologies that pick up the signals of any phone in the area—not just a suspect's.

"It's not a particularized surveillance device," said Jessica Price, a staff attorney at the Los Angeles branch of the American Civil Liberties Union (ACLU). "The ability to collect such massive amounts of data on innocent people is perhaps one of the most problematic pieces of this because it doesn't require that agencies target a particular phone number."

According to the public records obtained by USA Today, over 120 departments spanning 33 states use technology that allows them to collect the information of "thousands of cellphone users at a time," even though they may be be targeting just one number. Around one in four departments use a method of data collection known as a "tower dump," which utilizes cell company data to track all the users whose phones ping one or more targeted towers. Agents can then use a device known as a StingRay, which mimics a cell phone tower and allows them to track a specific signal's location, often down to just a few meters.

According to the report, more than 50 StingRay machines, which can cost as much as $400,000, were identified in departments stretching from California to Florida over the past two years, though the extent of their use remains largely shrouded in secrecy thanks to non-disclosure agreements with the FBI and with private manufacturers. The suitcase-sized devices are generally stored in vans for mobility, and are made available to local departments through state surveillance units, with federal funding made available through anti-terror grants.

StingRays do not collect the content of phone calls, but expensive upgrades can give departments that capability, Price told ATTN:.

Other bulk data collection programs used by the NSA have been defended for the potential severity and magnitude of crime they are employed to prevent. But some departments that use cell phone tracking technology, the report found, use cell-site simulators with a regularity impossible to justify for the same reasons. In Baltimore, for example, police used StingRay devices more than 4,300 times since 2007, according to recent testimony from a detective on the force. Departments can share how much they use StingRays, but refuse to disclose on which individual cases agents used them. According to police surveillance records obtained by USA Today and matched to court records, those individual case can involve either rape and homicide or cell phone theft.

StingRays pose a number of legal challenges both in and out of the courtroom. Though cell phone companies generally require court orders before police can access their phone records, StingRay devices operate as a pseudo-cell tower owned and operated by law enforcement, and can skirt such legal hurdles. But even in cases where they are used, officials often do not make it known to attorneys and judges that a StingRay was used to collect evidence, thanks to binding secrecy agreements between local departments and federal agents. One such agreement in Florida, obtained by the Guardian in April, reads:

The Florida Department of Law Enforcement will, at the request of the FBI, seek dismissal of the case in lieu of providing, or allowing others to use or provide, any information concerning the Harris Corporation [manufacturer] wireless collection equipment/technology, its associated software, operating manuals, and any related documentation.

There are also non-disclosure agreements between the private manufacturer and clients—Santa Clara County, California, made news recently when it refused to agree to a Harris Corporation agreement.

In cases where StingRay use has been at risk of being disclosed, prosecutors have dropped the case rather than risk discussing details in court proceedings. In some cases, when use has been disclosed, judges have tossed out evidence based on warrantless collection, the USA Today investigation noted. According to the investigation, the need for a warrant varies state-by-state, but in Baltimore, police used "pen register" orders, which must be judge-approved, but which do not require the same level of proof as a warrant. But according to Price, even when law enforcement agencies do apply for approval, they do not necessarily disclose that a search might include the use of a StingRay, which "exempts law enforcement agencies from a very important level of judicial scrutiny because a judge is supposed to sign off on any sort of search, certainly in this context where the search could be quite broad," Price told ATTN:.

For its part, the FBI maintains that its non-disclosure agreements do not prevent departments from disclosing that StingRay devices were used, according to statements made to the Washington Post in May, but as the USA Today investigation found, departments are less likely to discuss the particulars of the individual cases.

According to Price, that discrepancy poses some fundamental problems. "Because of the secrecy, it hinders the public's ability to assess the effectiveness of technology that our law enforcement wants to use," she told ATTN:. "And the public's ability to assess that is important in holding government accountable."

"We have a long tradition in this country of protecting privacy when you are in your home, or in private spaces. This technology enables the government to penetrate the walls that you would otherwise consider create privacy," she added.