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ST. LOUIS • Just one day before a city police officer was to face questions about a secret device used to locate suspects in a violent robbery spree, prosecutors dropped more than a dozen charges against the three defendants.

The move this month freed the officer from having to testify about a highly controversial surveillance tool — one that is subject to a confidentiality agreement between the St. Louis police and the FBI.

Prosecutors insist the charges’ dismissal was unrelated to the impending inquiry. But a public defender who intended to ask some of the questions believes otherwise.

Either way, the case has cast attention on use of “cell site simulators,” which can mimic a cell system tower, or screen data flowing through it, allowing a cellphone to be tracked to even a particular room.

Local police using them have accepted FBI demands for secrecy, even though details about the devices are widely available on the Internet.

Officials across the U.S. have been willing to drop cases rather than subject the technology to scrutiny by judges and defense lawyers. Civil libertarians complain that the hardware amounts to a warrantless search of countless properties.

The FBI calls it a matter of national security.

The FBI declined to say who is using cell site simulators in the area. St. Louis police wouldn’t answer questions about it. A spokeswoman for Circuit Attorney Jennifer Joyce’s office also declined to answer detailed questions but denied there was any connection between the charges’ dismissal and the officer’s impending deposition.

Documents dismissing the three robbery cases say simply that “continuing investigation has disclosed evidence which diminishes the prosecutive merits of this case.”

But Megan Beesley, the public defender, said she is convinced that prosecutors dropped the cases rather than allow defense lawyers to question a police Intelligence Unit officer about whether a simulator, often called by the brand name StingRay, was used here.

A STICKUP SPREE

Seven people were robbed of cash and cellphones in under two hours the evening of Oct. 28, 2013, starting in the 800 block of South Second Street and spreading to 17th and Chestnut streets and North 14th and Carr streets.

The next day, investigators traced at least one of the victims’ phones to Room 210 of the America’s Best Inn in Caseyville. Three men from East St. Louis and a woman from St. Charles were later charged with 14 counts of first-degree robbery and armed criminal action.

Beesley and two other defense lawyers became curious after reading in a report that a “proven law enforcement technique” had located the phone.

Asked about the phrase in a deposition Nov. 7, 2014, and a hearing March 31, Detective John Anderson said he could not answer. He cited a nondisclosure agreement and the fact he received the information from the police Intelligence Unit.

Defense lawyers scheduled a deposition April 9 to ask an intelligence officer under oath about StingRay. But the charges were dismissed April 8 against all but the female defendant. She had already admitted the crimes and agreed to testify against the others but now wants to rescind her guilty plea.

Brandon Pavelich, who was pistol-whipped in one of the robberies and required 18 stitches, said he was “shocked” when prosecutors told him the charges were dropped and explained only that “legal issues” had developed.

POORLY KEPT SECRET

StingRays, around for a decade, are a poorly kept secret, given revelations in courts, news stories and online descriptions. They once were used solely by federal agents.

When the Harris Corp. wanted to sell its product to local departments, it needed approval from the Federal Communications Commission, according to Nathan Freed Wessler, a staff attorney with the American Civil Liberties Union’s Project on Speech, Privacy, and Technology. The FCC wanted an overseer, so the FBI became involved and demanded strict nondisclosure agreements.

Court battles revealed such unredacted agreements for the first time this month, in Baltimore, Erie County, N.Y., and other places. The documents instruct those agencies to reveal no “information concerning the wireless equipment/technology” to the public — nor to other police departments or in court documents or proceedings without the FBI’s written approval.

If there is a risk of disclosure, the documents say, local officials are to notify the FBI so it can try to intervene, possibly encouraging local authorities to seek dismissal of charges or withdrawal of evidence.

The ability to track cellphones through their service providers’ antenna network is commonly known and is openly discussed in court and on TV shows. But the full capabilities of the StingRay are not clear.

Wessler said in an interview by telephone and email, “When a cell provider pings a phone, they can sometimes get GPS-level accuracy, but if police drive the StingRay around, they can pinpoint a cellphone’s location to a room within a building.”

He said the devices can obtain “precise location information about phones, including inside homes and other private spaces” and at the same time “conduct a dragnet search of bystanders’ phones in the area.” They can also disrupt service for some customers.

Civil libertarians are especially concerned about that collection of data from people not connected to a case.

Some police departments have said that they don’t store the data, but the details are unclear, Wessler said. He said it does not appear that cell site simulators available to local police can overhear calls or read texts or emails, although the most advanced versions available to the federal government can.

THE FBI RESPONDS

FBI spokesman Christopher Allen said in a telephone interview that the existence of StingRays is not considered sensitive — just how they work. He declined to answer questions.

The bureau supplied an April 2014 affidavit from Supervisory Special Agent Bradley Morrison, chief of the Tracking Technology Unit. He wrote that “cell site simulators are exempt from (court) discovery pursuant to the ‘law enforcement sensitive’ qualified evidentiary privilege” and also not subject to freedom of information laws.

Any FBI information shared with local authorities “is considered homeland security information,” he wrote. He warned that targets of investigation could benefit from piecing together minor details, “much like a jigsaw puzzle.”

Wessler, of the ACLU, said the FBI’s stance “certainly makes no sense today when it’s no secret that our cellphone locations can be tracked” with StingRays and other methods.

“So I think that the real reason is that this is an example of secrecy serving impunity,” he said. He suggested that it’s much easier to use intrusive technology when there’s less chance a judge or defense lawyer will object.

“But that’s the intent of the Fourth Amendment — to make police’s job harder by ensuring our rights aren’t being trampled,” he said.

STINGRAYS IN ST. LOUIS

In 2011, St. Louis police approached prosecutors and the court to work out procedures for using a loaner StingRay, said Circuit Court Judge Jack Garvey, who was part of the discussions. He praised police and prosecutors for their efforts to find the appropriate way to authorize StingRay use.

Police mainly used the device to locate crime victims’ cellphones, with the owners’ permission, Garvey explained. He said he was familiar with the technology, and signed administrative search warrants to authorize its use.

In 2012, St. Louis police sought bids for their own StingRay II in an SUV. It is not clear whether the purchase went through.

The court orders used now in St. Louis require a lesser standard of evidence and do not specifically mention cell site simulators, instead favoring this dense language: “Twenty-four hour a day assistance to include switch based solutions including precision location pursuant to probable cause based information queries and all reasonable assistance to permit the aforementioned Agencies to triangulate target location, including but not limited to terminating interfering service on the target telephone.”

Wessler said the description is “misleading” and legally insufficient, in part because it “doesn’t suggest that police will be using their own invasive equipment to conduct the tracking.”

ACCOUNTABILITY SOUGHT

The ACLU believes a search warrant should be obtained for each use, and should include information on the collection of bystanders’ data and restrictions on the retention of the data and the range of the device.

Wessler said the bulk collection of data could provide additional grounds for challenge, if a judge’s order says essentially that, “cops are allowed to drive around and search every house” and building electronically to find one cellphone.

He said StingRay is “forcing every phone ... to transmit information that they wouldn’t otherwise be transmitting,” such as unique identifying numbers.

It’s not clear when, or why, the orders were changed to become less specific, or how often they are approved.

Several judges who would likely handle the bulk of the requests estimate they have approved 80 of them in the first quarter of 2015, a court spokesman said. But judges were not told what method of gathering phone data would be used.

Presiding Judge Bryan Hettenbach said he would authorize use of a StingRay and wasn’t troubled by the lack of disclosure in the court orders. But he said he would be troubled by any “deliberate failure to disclose the (use of the technology) once the defendant was arrested and charged.”

He added, “The FBI cannot dictate, once a case is filed locally, what information is disclosed or not disclosed.”

FADING SECRECY

Wessler said changes are on the way in some places. In Mecklenburg County, N.C., prosecutors have said that they will notify defense attorneys about StingRays, and judges are demanding more information.

He said local police likely are putting “enormous pressure” on the FBI to relax some of the secrecy, to ease a “very uncomfortable” choice between using the StingRay and risking loss of evidence or not using hardware that cost hundreds of thousands of dollars.

“We’ll see what happens, but the secrecy regime is crumbling, and I think it cannot be sustained for much longer,” he said.

Wessler said the ACLU has identified 50 state and local agencies in 21 states and Washington that bought StingRay-type devices. “That’s an undercount because the secrecy is intense,” he noted. He said St. Louis is listed as “probable.”

He also said that thanks to the secrecy, there have been no legal challenges to the constitutionality of cell site simulators — so far.

CHALLENGES TO COME

When officials were setting up procedures in St. Louis, Garvey said, he remarked, “What are you going to do when the defense attorneys ask about it? You’re going to have to tell them.”

He said police officials responding by saying, “We’ll just see what happens.”

“It was a major concern, but it was premature,” Garvey said. He never expected the issue would take four years to surface. “I just can’t believe it’s taken this long.”

Five criminal defense lawyers who frequently appear in St. Louis courts told a reporter they were not aware of any cases involving a StingRay.

Beesley’s colleagues have found the “proven law enforcement technique” phrase used in four other pending cases and are planning on launching challenges in those cases.

“Now my office is on notice,” she said.

One thing not in dispute is StingRay’s effectiveness.

Said Garvey: “If they would just reveal it, you’ll find out the technology’s sound ... although it’s sci-fi.”

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