The Supreme Court of Wisconsin has upheld the warrantless use of cell phone tracking devices, better known as "stingrays.” In a narrow decision published on Thursday, the court found that while the Milwaukee police did not specifically have a warrant to use the stingray to locate a murder suspect, it did have a related judicial order that essentially served the same purpose.

This 2009 murder case is one of the rare, high-level court decisions that directly speaks to the legality of the use of stingrays, which are often used to track suspects’ phones and, in some cases, intercept calls and text messages. However, stingrays also capture related information on all other cell phone users who happen to be in physical proximity to the target.

The court order specifically approved “the installation and use of a trap and trace device or process,” and "the installation and use of a pen register device/process," and “the release of subscriber information, incoming and outgoing call detail…and authorizing the identification of the physical location of a target cellular phone.”

Earlier this year, Wisconsin passed a new law that specifically requires a probable cause warrant in order to track someone’s phone. That law was not in effect at the time of the 2009 murder.

Don't let sleeping murder suspects lie

The case goes back to June 9, 2009, when Milwaukee police responded to a shooting at a local mart. According to the state Supreme Court’s decision, “officers found a victim lying between the curb and the sidewalk with a fatal gunshot wound to the head. A second victim was taken to the hospital to receive treatment for a gunshot wound to his left ankle.”

Surveillance camera footage showed that the description of the shooter provided by witnesses matched a man in a striped polo shirt who had just purchased a prepaid cellphone and had told the clerk that his name was Bobby and that he’d just been released from prison that day.

Based on an affidavit filed by a police detective, the Milwaukee County District Attorney asked for and received a court order to locate the phone, and by extension, the suspect.

At trial, Officer Brian Brosseau of the Milwaukee County's Intelligence Fusion Center testified that after receiving cell site information from US Cellular, that phone’s provider, law enforcement then used a stingray “to further narrow down the phone’s location.” Eventually, police began knocking on doors at a particular apartment building, and eventually found Bobby Tate, asleep. He was still wearing the same striped polo shirt seen in the video, had blood-stained shoes, and had the phone the police were looking for—and was arrested on suspicion of first-degree homicide.

In court, Tate moved to suppress the evidence stemming from the order that authorized the cell phone tracking. When that motion was denied, he pleaded no contest, but appealed the suppression decision to an appellate court, which upheld the conviction. He finally appealed to Wisconsin's highest court and lost again.

Probable cause, probably

Legal experts pointed out that while this is a rare decision involving the use of stingrays, its narrowness likely won’t impact other cases.

“The government conceded that this was a search and that a warrant was required, so that issue was not before the court,” Orin Kerr, a law professor at George Washington University, and a former federal prosecutor, told Ars. “The court included a section pondering the issue anyway, even though the issue was not before them, in which they noted that it's not an easy question. But that's just what we lawyers call ‘dicta,’ a remark by the way, not actually part of the court's holding. The actual holding is that the order the government obtained was a warrant for Fourth Amendment purposes.”

Hanni Fakhoury , a former public defender and now a lawyer with the Electronic Frontier Foundation, told Ars that a major problem here was that the Supreme Court of Wisconsin should not have equated the pen register order with a warrant, as they have differing legal requirements.

“It assumes the tracking technology is a ‘search’ (the government conceded as much) but then equates a pen register order with a search warrant and finds there was probable cause,” he said. “It talks a lot about there being probable cause but if the statutory authority was that used for a pen register, Wisconsin Statute 968.35 only requires a showing that evidence is ‘relevant to an ongoing criminal investigation’ in order to use a pen register. That’s not probable cause.”

Worse still, the Supreme Court of Wisconsin appeared to have a limited knowledge of what data was collected, how it was transmitted to law enforcement, or how it was used to ultimately find the suspect via the stingray.

“It is not clear from the record exactly how law enforcement used cell site information in the present case,” the court wrote in its majority opinion. “We do not know whether US Cellular or law enforcement triangulated the signals from the target phone. We also do not know whether US Cellular regularly collects this information, or if it did so solely at law enforcement's request."

Nathan Wessler, an attorney with the American Civil Liberties Union, also highlighted this seeming misunderstanding of the technology itself.

“Even in the majority opinion they based their limited discussion of the stingray to testimony from the trial court,” he told Ars. “They mischaracterized how a stingray works. Yes, it tracks just a specific subject, but, as you well know, it also sends out a signal to every phone in the area. They don't fully understand the privacy implications of the technology.”

The ACLU recently uncovered documents from one local Florida police department to another clearly showing that cops have been deceiving courts about the use of stingrays.

“The point in time where giving full and accurate information matters the most is when the government is asking for the warrant,” Wessler added. “In that context there is an affirmative legal obligation to give full and accurate information to the judge. If a judge doesn't know what the privacy implications are for a new technology, it's impossible for them to issue a warrant that appropriately regulates the use of that technology.”