The new orders, sometimes called “geofence” warrants, specify an area and a time period, and Google gathers information from Sensorvault about the devices that were there. It labels them with anonymous ID numbers, and detectives look at locations and movement patterns to see if any appear relevant to the crime. Once they narrow the field to a few devices they think belong to suspects or witnesses, Google reveals the users’ names and other information.
‘‘There are privacy concerns that we all have with our phones being tracked — and when those kinds of issues are relevant in a criminal case, that should give everybody serious pause,” said Catherine Turner, a Minnesota defense lawyer who is handling a caseinvolving the technique. Investigators who spoke with The New York Times said they had not sent geofence warrants to companies other than Google, and Apple said it did not have the ability to perform those searches.
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Mr. Molina, 24, said he was shocked when the police told him they suspected him of murder, and he was surprised at their ability to arrest him based largely on data.
“I just kept thinking, You’re innocent, so you’re going to get out,” he said, but he added that he worried that it could take months or years to be exonerated. “I was scared,” he said.
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But despite the drawbacks, detectives noted how precise the data was and how it was collected even when people weren’t making calls or using apps — both improvements over tracking that relies on cell towers.
“It shows the whole pattern of life,” said Mark Bruley, the deputy police chief in Brooklyn Park, Minn., where investigators have been using the technique since this fall. “That’s the game changer for law enforcement.”