A Baltimore judge has tossed crucial evidence obtained via a stingray in a murder case—the trial was set to begin this week.

According to the Baltimore Sun, local police used the device, also known as a cell-site simulator, to locate the murder suspect in an apartment near his victim’s. In 2014, investigators used the stingray to locate the suspect, Robert Copes, who allowed them into his apartment. There, amid cleaning supplies including bleach and the phone they were looking for, police found the blood of Ina Jenkins, 34, in Copes' apartment. Jenkins' body was found “dumped across the street.”

The Baltimore police had a court-approved pen register, a legal authorization, to use the stingray. However that is not the same as a search warrant that requires probable cause.

Circuit Judge Yolanda Tanner said in court Monday that while she is suppressing the evidence “with great reluctance,” Copes is “likely guilty.”

"It was nonetheless an unconstitutional search," Tanner said, according to the Sun. "I can't play the 'what if' game with the Constitution.”

This case marks yet another example of judges pushing back against warrantless uses of the powerful surveillance device. In recent years, stingray use has come under increasing scrutiny, with several states including California, Washington, Virginia, Minnesota, and Utah now requiring a warrant for their use. Last year, the Department of Homeland Security and the Department of Justice also imposed new policies that mandate a warrant for stingray use in most cases.

Last month, the Maryland Court of Special Appeals published a legal opinion finding that state police must not only obtain a warrant before deploying a cell-site simulator but must also fully explain to the court what the device does and how it is used. Back in 2014, a Baltimore robbery case was dropped when the defendant challenged the use of a stingray.

As Ars has reported, stingrays can be used to determine a mobile phone’s location by spoofing a cell tower. In some cases, they can even intercept calls and text messages. Once deployed, the devices intercept data from a target phone along with information from other phones within the vicinity. At times, police have falsely claimed the use of a confidential informant when they have actually deployed these particularly sweeping and intrusive surveillance tools.

A similar case also examining the warrantless use of stingrays, known as United States v. Patrick, is currently pending before the 7th Circuit Court of Appeals in Chicago. When that opinion is handed down later this year or next year, it will be the first such ruling in a federal appellate court.