In August 2012, the Metropolitan Police Department (MPD) in Washington, DC entered into a secret agreement with the FBI.

The MPD was promising not to disclose any details about its use of a highly controversial antiterrorism surveillance technology known as a Stingray. About the size of a suitcase, the Stingray simulates a cell phone tower and intercepts mobile phone calls and text messages.

The MPD also agreed that if the department learned that any technical details about the surveillance technology was at risk of being exposed during a judicial proceeding, MPD would contact the FBI so the bureau could ask MPD to "seek dismissal of the case" in order to continue protecting the overall secrecy of the Stingray.

The unusual and potentially illegal arrangement between the FBI and MPD was memorialized in a six-page non-disclosure agreement (NDA) signed by MPD Assistant Chief Peter Newsham [pdf at the end of this story] after the police department requested "certain wireless collection equipment/technology" — what is commonly called the Stingray — manufactured by Harris Corporation, a Florida-based defense contractor.

"Consistent with the conditions on the equipment authorization granted to Harris Corporation by the Federal Communications Commission (FCC), state and local law enforcement agencies must coordinate with the Federal Bureau of Investigation to complete this non-disclosure agreement prior to the acquisition and use of the equipment/technology authorized by the FCC authorization," states the August 17, 2012 NDA sent to Newsham by the FBI.

The NDA, marked "law enforcement sensitive," was obtained by VICE News in response to a Freedom of Information Act (FOIA) request that kicked off a two-year battle with the police department in which the FBI intervened and blocked the release of the document and other records. The partially redacted NDA was finally turned over after VICE News' FOIA attorney, Jeffrey Light, successfully appealed the matter to the Washington, DC mayor's office.

Identical NDAs were released earlier this year in Maryland, New York, Florida, and Washington in response to open records requests and court orders that were part of a wide-ranging effort by civil liberties groups, privacy advocates, and journalists to pry loose information about how local law enforcement uses the Stingray devices.

"These NDAs are the keystone in this very corrosive regime of secrecy that both interferes with the public's ability to know what their local police departments are doing, but also interferes with defendants' due process rights in individual cases," said Nathan Wessler, an attorney with the ACLU's Speech, Privacy & Technology Project. "So it is significant when Metropolitan Police Department releases this document, because that will give public defenders in the city a better sense of why they haven't gotten disclosures in individual cases when Stingrays may have been used. It will give members of the public the basis of which to question their local government's secret activities. Every new disclosure sheds light and makes it more likely that local police will be held accountable."

The purpose of the surveillance technology is to combat terrorism. But according to a document turned over to VICE News last year — MPD's use of a Stingray was first revealed by VICE News in October — MPD planned to use the Stingray to increase the arrests of "fugitives, drug traffickers, and violent offenders (robbery, assault with a deadly weapon, Homicide), while reducing the time it takes to locate dangerous offenders that need to be removed from the streets of DC."

Wessler said last year that the Fourth Amendment rights of tens of thousands of DC residents are likely violated whenever DC police use Stingray, which sends out a more powerful signal than a cell tower and forces all mobile devices to report back serial numbers and locations.

MPD had obtained the Stingray in 2003 after being awarded a $260,000 Department of Homeland Security (DHS) grant. But the device sat unused in an "Electronic Surveillance Unit equipment vault" at the department for more than five years because the police department couldn't come up with the several thousands dollars it needed to train officers how to use it. In 2008, after securing another DHS grant, MPD dusted off and upgraded its Stingray.

According to other documents obtained by VICE News, MPD purchased a maintenance and training package last year from Harris Corporation for about $24,000, indicating the Stingray is still in use. (Each Stingray costs several hundred thousand dollars.) MPD redacted a majority of the information contained in the documents related to itemized costs of the training and maintenance, and a description of services — most of which is publicly available.

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Efforts by journalists and groups like the ACLU to find out how law enforcement has used Stingrays have largely been thwarted because the FBI has intervened in all of the FOIA cases.

Indeed, the NDA says that if MPD receives a FOIA request seeking information about the Stingray, its operating manuals, its software, "and any related documentation," the MPD "will immediately notify the FBI of any such request telephonically and in writing in order to allow sufficient time for the FBI to seek to prevent disclosure through appropriate channels."

That's exactly what transpired in response to VICE News' FOIA request.

In a March 24 email to VICE News, Sarah Jane Forman, associate director of the Mayor's Office of Legal Counsel, said decisions about whether Stingray-related documents, including operator manuals and the NDA, would be turned over to us "has been delayed because the Federal Bureau of Investigations has intervened and we are awaiting a response from them and the MPD."

On May 4, Ronald Harris, MPD's deputy general counsel, submitted a three-page letter to Forman explaining that the FBI submitted a "detailed letter setting forth the basis for withholding" information about the MPD's use of Stingray. The FBI told Harris that it could not disclose the NDA and other Stingray documents to VICE News. MPD withheld the FBI's letter that explained why.

Harris wrote in his letter that "release of the [Stingray] information and the NDA, as explained in the [FBI's] letter would provide information to persons intent on violating the law that could assist them in evading detection."

He added that the FBI explained in its letter that cell site simulator manufactures like the Harris Corporation have "classified their devices as regulated defense articles on the United States Munitions List."

"Accordingly, technical details related to the technology are subject to the non-disclosure provisions of the [Arms Control Export Act and International Traffic in Arms Regulation]," Harris said.

On May 29, the Mayor's Office of Legal Counsel partially reversed MPD's decision and ordered the release of the NDA — but allowed the department to withhold operators' manuals and other documents. It took the department four months to finally disclose the August 2012 NDA. VICE News is still awaiting the release of about 900 emails from MPD, which are currently being reviewed by the FBI.

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Laura Donohue, a law professor at Georgetown University and the director of the school's Center on National Security and the Lawand Center on Privacy & Technology, reviewed the NDA.

"It is extraordinary in that it uses private companies to override federalism and directs local law enforcement to hide information from judges during both the warrant procedure and in subsequent proceedings," she said. "[The FBI is] telling state and local enforcement what they can and cannot do in contracting with a private company…. They're using industry to control the police, and in the process overriding the judiciary. The real shock is that they're hiding it from the judges."

The NDA said details about the use of Stingrays needs to be shielded from disclosure, even from judges, because if individuals under investigation learned of its use they could employ "countermeasures to avoid detection by law enforcement."

"This would not only potentially endanger lives and physical safety of law enforcement officers and other individuals, but also adversely impact criminal and national security investigations," the NDA says. "Disclosure of this information could result in the FBI's inability to protect the public from terrorism and other criminal activity because, through public disclosures, this technology has been rendered essentially useless."

But Wessler said the FBI is trying to have its cake and eat it to.

[The bureau] is trying to say out of one side of its mouth that this is a super-secret national security tool," he said, "while on the other side of its mouth it says to every state and local law enforcement agency that comes asking, 'Oh yeah, sure, go ahead and use this — and you can use it to track down stolen cell phones, petty theft, and missing persons.' That does not describe to me a super-secret national security tool."

Wessler explained that the FBI's role in concealing information about the devices was the result of a directive by the FCC. In order for the Harris Corporation to sell the devices to state and local law enforcement agencies, it has to get special licenses from the FCC.

"Every time Harris has a new version of this technology, they have to go back to the FCC and get a new license," Wessler said. "The FCC, in granting that license, said the FBI has to sign off on each sale. The FBI, on its own say-so, interpreted that authority to sign off as an authority to impose these NDAs."

The FBI has since tried to walk back some language contained in its NDA, particularly references to the bureau's intervention in criminal cases. Last May, the publication Ars Technica obtained a statement from the FBI when another NDA was disclosed.

"The NDA should not be construed to prevent a law enforcement officer from disclosing to the court or a prosecutor the fact that this technology was used in a particular case," the statement said. "Defendants have a legal right to challenge the use of electronic surveillance devices, and not disclosing their use could inappropriately and adversely affect a defendant's right to challenge the use of the equipment."

Yet, it's been reported by Ars Technica that prosecutors in Baltimore dropped key evidence in a criminal trial in order to avoid explaining Stingray use and how it likely allowed law enforcement to locate a robbery suspect's phone. In other criminal cases, defendants were offered lenient plea deals so prosecutors would not be forced to reveal in court that Stingrays were used.

Washington, DC is unique among US cities in that the US Attorney's office prosecutes a majority of the adult felony criminal and misdemeanor cases. It would be extraordinary if the FBI and/or MPD were successful in convincing a federal prosecutor to abandon a criminal case or to strike lenient plea deals with defendants in cases where a Stingray was used.

A spokesman for the US Attorney's office in Washington, DC, did not respond to a request for comment on whether that ever happened.

"We are unaware of any instances where we have prosecuted a case or a case has been presented to us that incorporated Stingray evidence, and are also unaware of any examples of the FBI attempting to intervene in this fashion in any of our cases," said Robert Marus, a spokesman for the Office of the Attorney General in Washington, DC, which handles DUI, traffic, and some weapons-related cases.

While the NDA says that MPD has the statutory authority to use the Stingray, MPD spokeswoman Gwendolyn Crump would not respond to a question about the statutory source of that authority.

Recently, the Department of Justice issued guidelines on the use of Stingrays. Wessler said it's a "step in the right direction, but fails to address a number of important points."

"One of those important loopholes in the policy is that it doesn't apply to state and local agencies, including agencies that the FBI is overseeing — which is every single agency that buys one of these devices," he said.

Follow Jason Leopold on Twitter: @JasonLeopold