On Tuesday, Sept. 10, the Total Choice Credit Union in Laplace, Louisiana was robbed.

At approximately 3:06 pm, a man in his early thirties walked in wearing jeans, a white shirt, sunglasses, and a brown dreadlock wig, according to a now-unsealed complaint filed last month in US federal court. He passed a handwritten note to one of the tellers which read:

“ROBBERY. I DON’T WANT TO (HURT) OR (KILL) YOU OR ANYONE IN HERE SO I AM GOING TO GIVE YOU (FIVE SECONDS) TO (EMPTY) YOUR (REGISTER).”

The teller handed over more than $7,000 to the thief, who fled on foot.

Investigators canvassed the area for nearby surveillance cameras that might have picked up any clues. They found one with footage of an “older model white single-cab pickup truck stopped in the area directly behind the bank,” a minute or two before the robbery went down.

That’s when cops turned to a tool that has rendered the concept of a getaway car all but obsolete—the national network of automated license plate readers. These are fixed cameras with sensors that can be found in on utility poles, streetlights, overpasses, in police cars, even within traffic cones and digital speed display signs that show drivers how fast they’re going. The technology, known as ALPR, can clock roughly 2,000 plates a minute, on vehicles traveling up to 120 mph. Each license plate is photographed and the date, time, and location are recorded. Law enforcement can access a target’s movements in real time, or mine the data later to track a suspect’s daily patterns. ALPR systems cast an incredibly wide net that has made it far easier for cops to catch criminals. The method has also drawn harsh criticism from the American Civil Liberties Union (ACLU) and privacy advocates as “a technology deployed with too few rules,” and “a form of mass surveillance.”

There are few accurate estimates of the exact number of ALPRs across the US, which is a hodgepodge of local, state, and federal and tribal license plate readers. But occasional details do emerge. Through a records request, the ACLU discovered the New York police department operates roughly 500 license plate readers throughout New York City. In Los Angeles, police scan about 3 million plates per week, according to the Electronic Frontier Foundation (EFF), which says 200 separate agencies collected data on more than 2.5 billion license plates between 2016 and 2017. This data is all linked into a consolidated system run by the US Drug Enforcement Administration (DEA), which was first publicly revealed during a congressional hearing in 2012.

In the case of the Louisiana bank robbery, police keyed in a search for white single-cab pickup trucks in the area during the time period when the credit union robbery occurred. An ALPR located about 1 mile away from the bank captured a white 2001 GMC Sierra. The license plate showed it was registered to a New Orleans, LA man named Byron Watson—who happened to be on federal supervised release for robbing a Mansfield, Texas bank in 2012. In that case, Watson slipped the teller an almost identical note demanding the money be handed over within five seconds.

Through ALPR data, authorities gathered a detailed account of Watson’s alleged journey through Louisiana, the complaint says:

A statewide query on the A.L.P.R. system was conducted which revealed the following information: At approximately 10:10 A.M., the GMC Sierra was captured on North Robertson Street in New Orleans. At approximately 12:56 P.M., the GMC Sierra was captured on I-10E at the Laplace exit. At approximately 1:40 P.M., the GMC Sierra was captured in the City of Kenner on Loyola Avenue. At approximately 3:11 P.M., the GMC Sierra was captured on camera approximately 1.1 miles away from the bank. Finally, at approximately 4:45 P.M., the GMC Sierra was captured back in New Orleans at the Orleans Avenue exit on I-10W.

Surveillance footage from a subdivision adjacent to the bank completed the picture:

At approximately 3:00 P.M. the white truck was first observed as it turned onto Palmetto Drive before it turned right into the subdivision. The truck then made a u-turn and exited the subdivision. A short time later, the same truck repeated this maneuver, as if casing the nearby bank. The truck was then observed as it parked immediately behind the bank, but in a manner that concealed the vehicle from view of bank personnel and bank surveillance cameras. It should be noted that it is from this location that the suspect originated from on bank surveillance, as well as, the same direction the suspect fled toward after the robbery.

On Monday, Sept. 16, the FBI got a search warrant for Watson’s cellphone records. The data revealed that Watson’s phone “was communicating with towers in New Orleans, LA until approximately 10:50 AM.” It then switched to towers along the route from New Orleans to the scene of the crime, where Watson’s phone “began communicating exclusively with the four towers surrounding the Total Choice Credit Union in Laplace, LA.” The next ping from Watson’s phone was picked up in New Orleans at 3:46 pm, 40 minutes after the robbery. New Orleans, as it happens, is a 37-minute drive from Laplace.

On Thursday, Sept. 26, the Fidelity Bank in Jefferson, Louisiana was robbed. At about 3:06 pm, the same time the credit union in Laplace was robbed, a man walked in wearing jeans, a white shirt, sunglasses, and a black baseball cap. He handed the teller a handwritten note that read:

“I do not want to hurt anybody, give me all your money, you have 5 seconds.”

The teller gave $6,000 to the thief, who fled on foot.

Surveillance footage from inside the bank showed “numerous physical similarities” with Watson, and a camera outside captured footage of a white, older model single-cab pickup truck directly behind the building at the time of the robbery:

A statewide query on the A.L.P.R. system was conducted, on the aforementioned plate, which revealed the following information. At approximately 11:38 A.M., the GMC Sierra is captured on North Causeway Boulevard in Jefferson Parish. At approximately 12:45 P.M., approximately 23 minutes after the robbery, the GMC Sierra is captured on Airline Drive, as it exited Jefferson Parish. At approximately 12:55 P.M., the GMC Sierra is captured as it drove through the city of New Orleans.

Investigators called Watson’s probation officer in New Orleans, who told them that Watson had been scheduled to come in for a meeting the day of the Fidelity robbery but never showed up. Watson is currently detained, and is awaiting trial. His court-appointed attorney, Claude Kelly, did not immediately respond to a request for comment.

“Of course, technology can be useful in solving crimes,” Angel Diaz, a lawyer at the Brennan Center for Justice who is focused on the intersection of technology and civil liberties, told Quartz. “The problem is that the police don’t have rules in place that ensure their tools will only be used for these purposes. License plate readers can just as easily be used to track the movements of activists, religious minorities, and other historically marginalized groups.”

Dennis Franks, a retired FBI agent who now works as a security consultant, says the public doesn’t realize how much criminal activity is happening on the streets and would be “alarmed if they only knew.”

“As long as government authorities do not abuse the use of instruments such as ALPRs, they serve a vital role in helping protect society,” he says.

All else aside, says former New York City Police Department detective sergeant Joe Giacalone: “This complaint is a master course in using new technology, excellent investigation skills, and planning.”