An Arizona federal court this afternoon will be the battleground over the government's use of a "Stingray" surveillance device in a closely watched criminal case, United States v. Rigmaiden. And in an important development, new documents revealed after an ACLU of Northern California Freedom of Information Act (FOIA) request should leave the government with some explaining to do.

"Stingray" is the brand name of an International Mobile Subscriber Identity locator, or “IMSI catcher.” A Stingray acts as a fake cell-phone tower, small enough to fit in a van, allowing the government to route all network traffic to the fake tower. We've warned that Stingrays are dangerous because they have the capability to obtain the contents of electronic and wire communications while necessarily sucking down data on scores of innocent people along the way.

The Fourth Amendment requires searches be "reasonable," generally meaning they must be accompanied by a warrant. To get a warrant, the government must show there is probable cause to believe the place they want to search will have evidence of a crime. And it means the judge must ensure the warrant is "particular," or limited to only allow searches into areas where the evidence is most likely to be found. The only way a judge can make these tough decisions is with the government being forthright about what it's doing.

But when it comes to Stingrays the government has been extremely secretive about its use, withholding documents in FOIA requests, failing to explain (or even understand) the technology to a Texas federal judge and in Rigmaiden, misleading the court about the fact it's even using one at all.

Daniel David Rigmaiden is charged with a variety of tax and wire fraud crimes. Hoping to pinpoint Rigmaiden's precise location within an apartment complex, federal agents applied for an order requesting the court to order Verizon to help the agents pinpoint the physical location of a wireless broadband access card and cell phone they believed Rigmaiden was using. The order is clearly directed towards Verizon:

The Court therefore ORDERS, pursuant to Federal Rule of Criminal Procedure 41(b); Title 18, United States Code, Sections 2703 and 3117; and Title 28, United States Code, Section 1651, that Verizon Wireless, within ten (10) days of the signing of this Order and for a period not to exceed 30 days, unless extended by the Court, shall provide to agents of the FBI data and information obtained from the monitoring of transmissions related to the location of the Target Broadband Access Card/Cellular Telephone...

Ultimately, it turns out the government did not just get Verizon to give it the data. It also used a Stingray device to find Rigmaiden, sucking up loads of other data from other electronic devices in the complex as well, which it deleted.

When Rigmaiden filed a motion to suppress the Stingray evidence as a warrantless search in violation of the Fourth Amendment, the government responded that this order was a search warrant that authorized the government to use the Stingray. Together with the ACLU of Northern California and the ACLU, we filed an amicus brief in support of Rigmaiden, noting that this "order" wasn't a search warrant because it was directed towards Verizon, made no mention of an IMSI catcher or Stingray and didn't authorize the government—rather than Verizon—to do anything. Plus to the extent it captured loads of information from other people not suspected of criminal activity it was a "general warrant," the precise evil the Fourth Amendment was designed to prevent.

The FOIA documents bolster our argument that this isn't a warrant. The documents are a series of internal emails from DOJ attorneys in the United States Attorney's Office for the Northern District of California, the district where the order in Rigmaiden's case was issued. The emails make clear that U.S. Attorneys in the Northern California were using Stingrays but not informing magistrates of what exactly they were doing. And once the judges got wind of what was actually going on, they were none too pleased:

As some of you may be aware, our office has been working closely with the magistrate judges in an effort to address their collective concerns regarding whether a pen register is sufficient to authorize the use of law enforcement's WIT technology (a box that simulates a cell tower and can be placed inside a van to help pinpoint an individual's location with some specificity) to locate an individual. It has recently come to my attention that many agents are still using WIT technology in the field although the pen register application does not make that explicit. While we continue work on a long term fix for this problem, it is important that we are consistent and forthright in our pen register requests to the magistrates…

These emails, combined with the text of the disputed order itself, suggest agents obtained authorization to use a pen register without indicating they also planned to use a Stingray. Either at the time of the application or after the fact, the government attempted to transform that order into a warrant that authorized the use of a Stingray.

Judicial superivison of searches is most needed when the government uses new technologies to embark into new and unknown privacy intrusions. But when the government hides what it's really doing, it removes this important check on government power. We hope the court sees its been duped, and makes clear to the government that honesty and a warrant are requirements to using a Stingray.