(Bloomberg) -- After five people were killed in a 2020 arson in Colorado, law enforcement officials failed to turn up any leads through their initial investigative techniques. So they served a warrant to Google for anyone who had searched for the address of the fire, according to a court motion.

Google eventually complied with the data request, helping law enforcement find suspects. Three teenagers who had searched the address were charged with murder. But the technique also drew a challenge from defense lawyers, who are calling reverse keyword search warrants “a digital dragnet of immense proportions.” It’s the first case to challenge the constitutionality of the method, the attorneys say.

Defense lawyers filed a motion Wednesday to challenge the judge’s decision to use evidence from the warrant to charge their client, Gavin Seymour. They’re asking the Colorado Supreme Court to review the matter, after the judge earlier denied their motion to suppress the evidence.

The keyword search warrant “is profoundly different from traditional search warrants seeking data belonging to a suspect,” the defense argued in the court filing. “Instead, the process operates in reverse — search everyone first, and identify suspects later.”

A spokesperson for the Denver district attorney’s office declined to comment. Representatives for the Denver police department and Google did not immediately respond to requests for comment. 

Investigators secured three keyword search warrants. Google declined to comply with the first two but provided information in response to the third, according to the motion.

There are few known examples of keyword search warrants, but the practice has come under scrutiny in the wake of the US Supreme Court’s decision to overturn the right to abortion. Some advocates have expressed concern that keyword search warrants and geofence warrants, in which police turn to tech companies for information about users who visited a particular location, could be used to prosecute women who obtain abortions in states where it is illegal. 

In a transparency report containing information through 2020, Google said geofence warrants had been on the rise since 2018, adding that they represented more than a quarter of all warrant requests to the search giant in the US. 

Lawyers for the arson case defendant maintain that Google must search billions of users to respond to keyword search warrants, raising privacy implications far beyond Colorado.

“This is a really significant new legal issue with tremendous implications for not only Mr. Seymour but for everyone in the country who uses Google to run searches,” said Michael Price, Litigation Director for the Fourth Amendment Center at National Association of Criminal Defense Lawyers, who represents Seymour. 

--With assistance from Davey Alba and Jack Gillum.

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