Newly uncovered court documents in a federal armed New Jersey bank robbery case that went to trial in late February 2015 reveal an unusual back-and-forth between authorities and judges—ultimately resulting in the FBI seeking and getting a warrant to use a stingray. The move illustrates a rare known instance where authorities met the probable cause hurdle need for a warrant in a stingray deployment.

In 2012, federal prosecutors went to a judge to ask for a "pen/trap order," a lower type of permission than a warrant. Such an order would have effectively authorized the use of a stingray. But the judge pushed back and imposed usage restrictions "in a private place." In January 2015, two United States senators made public the FBI’s position that the agency could use stingrays in public places without a warrant.

Seemingly dissatisfied with this restriction, an FBI agent then took an unusual step—he swore in a new affidavit as part of a warrant application to a different judge for permission to deploy "mobile equipment." Such gear would enable the FBI "to monitor the dialing, routing, addressing, and signaling information of the Target Facility in order to determine its general location for a period of 30 days beginning within 14 days of the date of the warrant." The second judge, United States Magistrate Judge Mark Falk, signed off on the search warrant absent other limits.

Stingrays, the common name for "cell-site simulators," can be used to determine a phone’s location, but they can also intercept calls and text messages. During the act of locating a phone, stingrays also sweep up information about nearby phones—not just the target phone. Earlier this year, Ars reported on how the FBI is actively trying to "prevent disclosure" of how these devices are used in local jurisdictions across America.

"This is a good example of why it is so important for the government to provide full and accurate information about stingrays when applying for judicial orders," Nathan Wessler, an attorney with the American Civil Liberties Union, told Ars. "With accurate information, it is possible for judges to provide oversight; without accurate information, it is not."

"At the very minimum, police should be getting a warrant, and that warrant should be based on an application that provides a full description of the stingray's capabilities and impacts on third parties," Wessler continued. "Due to the first magistrate judge's diligence, that's what happened here, and that is a good thing. I would note, however, that it is an unsettled question in the courts whether even a warrant can appropriately constrain stingray use, given the dragnet quality of the search that occurs when the device gathers information from potentially large numbers of bystanders' phones."

Let's just call it: “Mobile Equipment”

Relatively little is known about how, exactly, the stingrays are used by law enforcement agencies nationwide, although documents have surfaced showing how they have been purchased and used in some limited instances. In 2013, Ars reported on leaked documents showing the existence of a body-worn stingray. Five years ago, Kristin Paget famously demonstrated a homemade device built for just $1,500.

Worse still, cops have lied to courts about the use of such technology. The largest manufacturer of the devices, the Harris Corporation, has been tight-lipped about its hardware capabilities.

"We do not comment on solutions we may or may not provide to classified [Department of Defense] or law enforcement agencies," Jim Burke, a spokesman for the Harris Corporation, previously told Ars.

The New Jersey case, known as United States v. Claude Williams, charges the suspect with three counts of bank robbery and two counts of use of a firearm in furtherance of a crime of violence. Federal prosecutors allege that he stole over $44,000 from three New Jersey banks in late 2011 and July 12, 2012.

Williams’ attorneys did not respond to Ars’ request for comment.

Just one day after the July 12, 2012 robbery, Osmar Benvenuto, an Assistant United States Attorney, filed a sealed pen register and trap and trace application to obtain more information about Williams. (It was later unsealed as part of court filings in 2014.)

Typically the legal process that local law enforcement uses to deploy stingrays involves asking a judge to sign off on a "pen register and trap and trace order." In the pre-cellphone era, a "pen/trap order" allowed law enforcement to obtain someone's calling metadata in near real-time from the telephone company. Now, that same data can also be gathered directly by the cops themselves through the use of a stingray. In some cases, police have gone to judges asking for such a device or have falsely claimed a confidential informant, but in fact have deployed this particularly sweeping and invasive surveillance tool.

Here, Benvenuto took the unusual step of more clearly articulating what the government wanted to do.

As he wrote:

I have been informed that this investigation may require the use of mobile pen register and trap and trace equipment ("the Mobile Equipment") capable of receiving, sending, and capturing the dialing, routing, addressing and signaling information that cellular telephones such as the Target Facility use to establish connections with Sprint's network, and of determining the general direction from which those signals are being broadcast. Generally, the Mobile Equipment may operate by mimicking one of Sprint's cell towers to get the Target Facility to connect to it, or it may simply screen signaling information going to or from Sprint's cell phone towers in the Mobile Equipment's immediate vicinity for dialing, routing, or addressing information emanating from or destined to the Target Facility. Once the Mobile Equipment detects the Target Facility's dialing, routing, addressing or signaling information (by virtue of the Target Facility's unique identifiers described above), the Mobile Equipment may display one or more of the paths from which the Target Facility's signals are received and the strength of those signals.

He also added this warning:

Because of the way the Mobile Equipment sometimes operates, its use has the potential to intermittently disrupt cellular service to a small fraction of Sprint's wireless customers within its immediate vicinity. Any potential service disruption will be brief and minimized by reasonably limiting the scope and duration of the use of the Mobile Equipment.

How private is private?

Most judges are likely to sign off on a pen register application, not fully understanding that police are actually asking for permission to use a stingray. Under federal law , pen registers are granted under a very low standard: authorities must simply show that the information obtained from the pen register is "relevant to an ongoing criminal investigation."

Getting a judge to authorize a pen register is a far lower standard than being forced to show probable cause for a search warrant or wiretap order. A wiretap requires law enforcement to not only specifically describe the alleged crimes but also to demonstrate that all other means of investigation had been exhausted or would fail if they were attempted.

But in this case, United States Magistrate Judge Patty Shwartz imposed this handwritten restriction.

"In no event [can the FBI] use the mobile equipment, absent other authority, to use the equipment to locate the Target Facility in any private place or where they have reason to believe the Target Facility is in a private place," she wrote.

Brian Owsley, who also held the position of US Magistrate in Texas before leaving the bench to become a law professor at Indiana Tech and has been outspoken on the issue of stingrays, told Ars that he found such a limit to be noteworthy.

"I think it is somewhat interesting that she limits it to a 'private place' whatever that is construed to be," he told Ars by e-mail. "I would interpret it to be in residence, but what about a business, doctor’s office, or private club?"

Shortly thereafter, FBI Special Agent Michael Scimeca wrote a nearly identical affidavit to a different judge in a search warrant application, which was approved.

Catherine Crump, a law professor at the University of California, Berkeley, told Ars that this type of disclosure and small restrictions are steps in the right direction.

"Stingrays are just one example of a technology that allows law enforcement agents unprecedented power to gather information about private citizens in secret, and the magistrate judges who are on the receiving end of government applications to engage in this sort of surveillance have an important role to play in making sure that the government complies with the law," she wrote by e-mail.

"Unfortunately, magistrate judges often face an uphill battle because only the government is involved in these proceedings," Crump said. "Recently there has been increased news coverage of stingrays, and I am hopeful that as their capabilities become better known, magistrate judges will be in a better position to evaluate the government’s arguments and push back against them when necessary."