On October 13th, 2018, two men walked into a Great Midwest Bank in a suburban strip mall outside Milwaukee. They were the first two customers when the bank opened, barely recognizable behind sunglasses and heavy beards — but it soon became clear what they were after. One man jumped onto the teller counter and pulled out a handgun, throwing down a garbage bag for the tellers to fill with money. They left the bank at 9:09AM, just seven minutes after they entered, carrying the bag full of cash, three drawers from the vault and teller station, and the keys to the bank vault itself.

In the months since, police and federal agents have struggled to track down the bank robbers. Local media sent out pictures from the bank’s security cameras, but it produced no leads. Finally, police hit on a more aggressive strategy: ask Google to track down the bank robbers’ phones.

In November, agents served Google with a search warrant, asking for data that would identify any Google user who had been within 100 feet of the bank during a half-hour block of time around the robbery. They were looking for the two men who had gone into the bank, as well as the driver who dropped off and picked up the crew, and would potentially be caught up in the same dragnet. It was an aggressive technique, scooping up every Android phone in the area and trusting police to find the right suspects in the mess of resulting data. But the court found it entirely legal, and it was returned as executed shortly after.

That kind of warrant, known as a reverse location search, has become increasingly common in recent years. More than 20 such warrants have been served in Minnesota, and at least one similar case came to light in North Carolina. Most controversially, the technique was used to identify suspects after a Proud Boy rally-turned-riot in midtown Manhattan last year.

In each case, police weren’t tracking the location of a specific suspect — where normal standards of reasonable suspicion would apply — but instead pulling the names of every individual who had been in the vicinity when a crime took place. For civil liberties groups, it’s a dangerous and potentially unconstitutional overreach of police power. But those concerns haven’t been enough to keep police from filing reverse location search warrants when a case runs dry, or to convince judges to reject them.

In the Wisconsin case, it’s not clear how useful that technique actually was. When The Verge reached out to the FBI’s Milwaukee division to ask if any charges had been brought, officers said the case was ongoing and they could not provide any additional information as a result. With nearly a year elapsed since the warrant was served, that suggests this particular reverse location search may not have been as fruitful as investigators hoped.

Groups like EFF have a lot of problems with this kind of search, particularly that it cuts against a Supreme Court precedent that treats location data as “an intimate window into a person’s life.” But the biggest gripe is the simple success rate: in the Wisconsin case, police asked for a dragnet that could produce that sensitive location data for dozens of people — but if the bank robbers weren’t using Google Maps or just left their phones at home, they wouldn’t show up in that search. For civil libertarians, that looks like a whole lot of suspicionless searches and nothing to show for it.