Should Google location data be a tool for cops?

Updated Evidence collected in a Google geofence dragnet warrant that's being used to prosecute a Virginia man accused of robbing a bank is unconstitutional and should be thrown out of court, according to the American Civil Liberties Union (ACLU) and eight federal public defenders. 

The groups filed an amicus brief in United States v. Chatrie, the first-ever geofence search case to reach a federal court of appeals, urging the judge to suppress this evidence, which they argue is illegal. 

They've also asked the court to address the larger issue of whether geofence warrants violate the Fourth Amendment, which protects against unreasonable searches and seizures by the government.

"This will provide law enforcement officers and magistrate judges with much-needed guidance, and guard against future unconstitutional searches," according to the court documents filed on Friday.

Google did not respond to The Register's request to comment for this story.

While we don't know how many geofence warrants Google services on a regular basis, we do know that it received more than 87,000 subpoenas and search warrants in 2021 (it hasn't yet published info for 2022).

To catch a thief

In 2019, someone robbed a Virginia credit union at gunpoint and left with $195,000 from a bank safe. To help find the suspect, police served Google with a geofence warrant [PDF] requesting location data for every Google device user within 150 meters of the bank an hour before and after the robbery. 

The cops eventually returned to Google and asked for specific information about three users including names, subscriber information, email addresses, electronic devices, and phone numbers associated with the accounts.

A geofence in an urban area that has a diameter longer than three football fields will sweep in an overwhelming number of people and devices for which there is no probable cause to search

A few months later, police arrested 27-year-old Okello Chatrie, who was charged with armed robbery.

In March, a federal judge ruled that the geofence warrant was too broad, and therefore violated Chatrie's constitutional protections [PDF]. 

However, the judge refused to toss the evidence citing the "good-faith exception" to the Fourth Amendment. This essentially says if the police believed in good faith that they were acting according to legal authority, then the evidence seized is admissible in court.

Good faith? Or illegal search?

And this is where the amicus brief comes into play. The ACLU and public defenders, in their court documents, challenge the judge's conclusion. They argue that "obvious" defects in the warrant, including its effect on the privacy of people with no connection to the crime, make it an illegal "general warrant," and as such, the good-faith exception does not apply.

"Geofence warrants like this one purport to authorize sweeping searches of an unidentified number of devices without particularized probable cause and without sufficient judicial oversight," the brief says. 

"Moreover, any officer would logically understand that where, as here, a geofence in an urban area has a diameter longer than three football fields, it will sweep in an overwhelming number of people and devices for which there is no probable cause to search," it adds.

Despite becoming more common — police used a geofence warrant in Minneapolis around the time of the George Floyd protests and, more recently, to identify people who stormed the US Capitol on January 6, 2021 — the use of these types of location-data dragnets are increasingly worrisome to data privacy advocates and some lawmakers alike.

• To catch a thief, go to Google with a geofence warrant – and it will give you all the details
• NSA asks Congress to let it get on with that warrantless data harvesting, again
• Hey, online pharmacies: Quit spreading around everyone's data already
• Here's US Homeland Security collaring a suspected arsonist after asking Google for the IP addresses of folks who made a specific search

EFF has also filed an amicus brief in the Chatrie case, and New York lawmakers last year proposed a bill to ban geofence reverse keyword search warrants. Tech giants including Google, Amazon, Microsoft and Meta have said they support a ban on these types of data-trawling techniques.

There's also a concern that these types of reverse location searches will be used to build criminal cases against women seeking abortions in states where the procedure is no longer legal.

Washington state lawmakers have taken up this cause, and bills introduced in both the House and Senate would, among other things, make it illegal to utilize a geofence around a facility that provides health care services [PDF].

The proposed Washington law would also make it illegal for period-tracking apps or any other website to sell consumers' health data while also making it harder for them to collect and share this personal information. ®

Updated to add

A Google spokesperson sent us the following statement after this story was published:

"As with all law enforcement demands, we have a rigorous process that is designed to protect the privacy of our users, including by pushing back on overly broad requests, while supporting the important work of law enforcement."

The tech giant declined to clarify if it supported a ban on geofence warrants. Make of that what you will.