(Update below)

A Justice Department document obtained by the ACLU of Northern California shows that federal investigators were routinely using a sophisticated cell phone tracking tool known as a "stingray," but hiding that fact from federal magistrate judges when asking for permission to do so.

Stingrays and similar devices essentially impersonate cell phone towers, allowing them to pinpoint the precise location of targeted cell phones (even inside people's homes) and intercept conversations. They also sweep up the data of innocent people who happen to be nearby. By withholding information about this technology from courts in applications for electronic surveillance orders, the federal government is essentially seeking to write its own search warrants.

If judges are going to approve surveillance, they need to be fully informed so they can decide whether it is appropriate. They also need the opportunity to require privacy safeguards, such as rules on how to handle the data of innocent people that may be captured by the devices as well.

Our receipt of the Justice Department document (through a Freedom of Information Act lawsuit filed along with the San Francisco Bay Guardian) came just in time. On Thursday, I will be arguing to a federal court in Arizona that it should disregard evidence produced by a stingray in the case of Daniel Rigmaiden, because the government used the tracking tool but failed to tell the federal magistrate judge that it was doing so. Rigmaiden has filed a motion to suppress evidence produced by the stingray, and the ACLU and the Electronic Frontier Foundation filed an amicus brief supporting that position (you can read our brief here).

The new document, which we submitted to the court late yesterday, shows that the government's troubling conduct in the Rigmaiden investigation was not isolated. The document contains an internal email string from the office of the United States Attorney for the Northern District of California (you can read the emails here). One of the emails reads:

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…

In other words, the federal government was routinely using stingray technology in the field, but failing to "make that explicit" in its applications to the court to engage in electronic surveillance. When the magistrate judges in the Northern District of California finally found out what was happening, they expressed "collective concerns," according to the emails. Notably, this email chain is dated May 2011, some three years after the Stingray's use in Rigmaiden's case – meaning the government was not "forthright" in its applications to federal magistrate judges for at least three years.

The government claimed in its brief opposing Rigmaiden's motion to suppress that at most there was an innocent mistake by agents "using a relatively new technology." In court Thursday, I will argue that this email confirms the need for suppressing the evidence in the Rigmaiden case because it shows that the government was engaged in a widespread practice of withholding important information for judges, and that it did so for years.

We hope that the court sends the clear message to the government that it cannot keep judges in the dark. Judges are not rubber stamps – they are constitutional safeguards of our privacy.

Update (March 29):

The court held a lengthy hearing on the motion to suppress. During the course of the argument, the judge pressed counsel for the government extensively on a number of issues, including whether the submissions by the government when it sought permission to use the stingray device provided sufficient information to the judge and whether the order that the government now claims was a warrant actually gave the government authorization to perform a search using the stingray. In addition, the judge raised questions about whether the government violated the protocol set forth in a warrant for searching Mr. Rigmaiden's laptop and if so, what the appropriate remedy would be. (We did not weigh in on this issue in our amicus brief.)

Significantly, the government stated in the course of the argument that "use of these devices is a very common practice." It also stated that there were many parts of the country in which the FBI successfully obtains authorization to use this device through a trap and trace order.

These two representations by the government are very interesting because it is very difficult to obtain information about the extent of the government's use of stingray devices, and the type of authorization the government obtains. These orders are typically under seal. There is a significant constitutional question whether stingray devices -- because they scoop up information of unrelated third parties -- can ever be used consistent with the Fourth Amendment, but at a minimum, the government should clearly be seeking a warrant based on probable cause before deploying the device.

The judge said he'd have a ruling in a few weeks.