OAKLAND, Calif.—A federal prosecutor seemed to trip up during a Wednesday court hearing in an attempted murder case. The reason? This prosecutor had to explain how cell-site simulators, sometimes known as stingrays, actually operate.

Joseph Alioto, the lead federal prosecutor, initially suggested that the suspect’s mobile phone company, MetroPCS, needed to somehow activate the Oakland Police Department’s stingray immediately following the January 21, 2013 shooting of a police officer. But that’s not how stingrays work—rather, they act as fake mobile phone towers and do not require any affirmative interaction on behalf of any phone company’s network.

Despite the mistake, the Wednesday hearing may prove to be a crucial one in the ongoing case of United States v. Ellis, where four men are charged with the 2013 attempted murder of local police officer Eric Karsseboom in a parking area near an East Oakland apartment complex. (One of those men, Damien McDaniel, pleaded guilty earlier this year.)

This case has now been running for over three-and-a-half years, and it may finally be entering a new phase: the judge could call for an evidentiary hearing where the intricacies of the stingray are more fully explored. In turn, that could pave the way for a firm trial date or plea deals (which Alioto said remain on the table). Either way, the court's next ruling likely will bring United States v. Ellis closer to its conclusion.

Confusion

Ellis has provided rare insight into how the stingray is used in practice to find suspects and the seeming lengths the government is willing to go to keep it quiet. The surveillance tool has come under increasing scrutiny by lawmakers and activists in recent years. Since this case began, the Department of Justice, which oversees the FBI, and the State of California now require a warrant when a stingray is used in most circumstances.

Moments after Alioto’s slip-up, one of his colleagues tried to step in.

"The cell-site simulator has the ability to simulate a cell tower regardless of what the phone company is doing," Scott Joiner, another Assistant United States Attorney, said.

In a previous hearing two years ago, Alioto firmly denied to the court that there were two stingrays used to locate one of the suspects, Purvis Ellis. This assertion has subsequently turned out not to be true.

Instead, the OPD used its stingray for several hours on January 21, 2013 in an immediate attempt to locate Ellis, who was suspected of being involved in the shooting. When that effort failed, the FBI was brought in. That organization then used its stingray—again without a warrant—to successfully locate Ellis.

Later on in the Wednesday hearing, Martha Boersch, Ellis’ defense attorney, said that Alioto had "confused" the relationship between the law enforcement agency and the phone company.

"The stingray operates completely independently of the phone company," she said. "You do not need a pen register order to operate a stingray. No phone company has to turn anything on."

Pen registers are historical mechanical devices that capture incoming and outgoing calls only. They were the key technological component in a famous 1979 Supreme Court case, Smith v. Maryland, where the court found that there was no "reasonable expectation of privacy" over a criminal suspect's dialed phone numbers. Therefore, no warrant was required.

Prior to the DOJ 2015 warrant requirement, many federal law enforcement agencies argued that the rules and precedents around pen registers simply applied to stingrays as well. According to this line of thought, stingrays were simply collecting calling metadata and location information—not content, which would fall under the more stringent federal wiretap law.