A routine request in Florida for public records regarding the use of a surveillance tool known as a stingray took an extraordinary turn recently when federal authorities seized the documents before police could release them.

The surprise move by the U.S. Marshals Service stunned the American Civil Liberties Union, which earlier this year filed the public records request with the Sarasota, Florida, police department for information detailing its use of the controversial surveillance tool.

The ACLU had an appointment last Tuesday to review documents pertaining to a case investigated by a Sarasota police detective. But marshals swooped in at the last minute to grab the records, claiming they belong to the U.S. Marshals Service and barring the police from releasing them.

ACLU staff attorney Nathan Freed Wessler called the move "truly extraordinary and beyond the worst transparency violations" the group has seen regarding documents detailing police use of the technology.

"This is consistent with what we've seen around the country with federal agencies trying to meddle with public requests for stingray information," Wessler said, noting that federal authorities have in other cases invoked the Homeland Security Act to prevent the release of such records. "The feds are working very hard to block any release of this information to the public."

Stingrays, also known as IMSI catchers, simulate a cellphone tower and trick nearby mobile devices into connecting with them, thereby revealing their location. A stingray can see and record a device’s unique ID number and traffic data, as well as information that points to its location. By moving a stingray around, authorities can triangulate a device’s location with greater precision than is possible using data obtained from a carrier’s fixed tower location.

The records sought by the ACLU are important because the organization has learned that a Florida police detective obtained permission to use a stingray simply by filing an application with the court under Florida’s “trap and trace” statute instead of obtaining a probable-cause warrant. Trap and trace orders generally are used to collect information from phone companies about telephone numbers received and called by a specific account. A stingray, however, can track the location of cell phones, including inside private spaces.

The government has long asserted it doesn’t need a probable-cause warrant to use stingrays because the device doesn’t collect the content of phone calls and text messages, but instead operates like pen-registers and trap-and-traces, collecting the equivalent of header information. The ACLU and others argue that the devices are more invasive than a trap-and-trace.

Recently, the Tallahassee police department revealed it had used stingrays at least 200 times since 2010 without telling any judge because the device’s manufacturer made the police department sign a non-disclosure agreement that police claim prevented them from disclosing use of the device to the courts.

The ACLU has filed numerous records requests with police departments around the country in an effort to uncover how often the devices are used and how often courts are told about them.

In the Sarasota case, the U.S. Marshals Service claimed it owned the records Sarasota police offered to the ACLU because it had deputized the detective in the case, making all documentation in the case federal property. Before the ACLU could view the documents Sarasota had put aside for them, the agency dispatched a marshal from its office in Tampa to seize the records and move them to an undisclosed location.

The U.S. Marshals Service declined to comment, saying it "does not discuss pending litigation."

Florida public records law requires that even if a dispute over records occurs, the Sarasota Police Department was legally obligated to hold onto the records for at least 30 days once it had received the ACLU’s request. That period would have given the ACLU a chance to argue its case in court to obtain the records.

"We’ve seen our fair share of federal government attempts to keep records about stingrays secret, but we’ve never seen an actual physical raid on state records in order to conceal them from public view," the ACLU wrote in a blog post today.

The ACLU filed an emergency motion seeking a temporary injunction preventing the police department from releasing additional files to the marshals. The motion also asks the court to find the department in violation of state law for allowing the U.S. Marshals Service to seize the documents. The ACLU wants the court to order the police department to retrieve the documents. Because the issue is a state matter and the ACLU filed the motion in a state court, the judge cannot directly order the U.S. Marshal Service, a federal agency, to return the documents.