Minnesota’s top law enforcement agency agreed to terms set by the FBI to resist any attempts by the public to gain information about controversial cellphone-tracking technology, according to documents obtained by the Star Tribune.

The revelation comes after a lengthy attempt to obtain contracts and nondisclosure agreements for the FBI’s cellphone tracking devices, known as StingRay II and KingFish. The state Bureau of Criminal Apprehension (BCA) has long resisted disclosure requests from the public, news media and even the Minnesota Legislature, saying that doing so would violate trade secrets and expose investigative techniques that could be exploited by criminals. The most recent documents were released to the Star Tribune only after the Information Policy Analysis Division, which interprets the state’s open records law, determined they could not be withheld in their entirety.

The tracking devices, which mimic local phone towers to capture data and location information of cellphones in a given area, are used by the BCA and the Hennepin County Sheriff’s Office. They’ve become a flash point nationally in the debate over the degree to which law enforcement’s investigative reach clashes with an individual’s right to privacy. Hundreds of American Civil Liberties Union affiliates have filed similar requests across the country.

In a heavily redacted 2012 contract signed by then-Assistant BCA Superintendent David Bjerga, the agency agreed to “immediately notify the FBI” of any request for information concerning the device’s manufacturer, Florida-based Harris Corp., under the Freedom of Information Act (FOIA), or under judicial, administrative or legislative requests.

Any court orders directing the BCA to reveal information about Harris Corp. “will immediately be provided to the FBI in order to allow sufficient time for the FBI to intervene to protect the equipment/technology and information from disclosure and potential compromise,” the contract reads.

Law enforcement’s use of the devices was brought to light by privacy and open-government advocate Rich Neumeister, who last year persuaded Hennepin County to release its contracts with Harris Corp. The BCA denied his request. Legislators’ interest was piqued after Neumeister’s efforts. In a letter to lawmakers, Minnesota Department of Public Safety Commissioner Mona Dohman said the department owns one Stingray II and one KingFish, used exclusively by the BCA. She said the department has spent $632,773 on the devices since 2005.

Neumeister’s efforts spurred bipartisan legislation passed this year that requires law enforcement to obtain a tracking warrant before the devices are deployed.

In a letter to the Star Tribune, BCA Assistant Superintendent Drew Evans explained that the documents, which include Harris Corp.’s lease of the equipment to the BCA, along with the FBI memo, are heavily redacted because they reveal investigative techniques and capabilities. Redaction involves blacking out information so it is not readable.

“This would not only endanger the lives and physical safety of law enforcement officers and other individuals, but also adversely impact criminal investigations,” Evans wrote. “Disclosure of this information could result in the BCA’s inability to protect the public from terrorism and other criminal activity because, through public disclosures, this technology has been rendered essentially useless for future investigations.”

Neumeister said the explanation fails to address a number of questions. For instance, because of the redactions in the lease, it is unclear specifically what kind of equipment is in use by the BCA, or who signed the lease for it.

“Why for 13 months have they denied us this public information, particularly when you look at the contract, which has nothing at all?” Neumeister said.