In this Oct. 22, 2018, photo U.S. Immigration and Customs Enforcement agents surround and detain a person during a raid in Richmond, Va. Credit: Steve Helber | AP

Immigration agents have been tapping into a vast, privately maintained database of license plates gleaned from vehicles across the United States to track down people who may be here illegally, according to documents obtained by the American Civil Liberties Union and released Wednesday.

The database contains billions of records on the details of vehicle locations captured from red-light and speed-limit cameras as well as from parking lots and toll roads that use the nearly ubiquitous and inexpensive scanners to monitor vehicle comings and goings.

Local police forces have long used those scanners to track criminal suspects and enforce traffic laws across the U.S. But the records the ACLU obtained from the Department of Homeland Security through a Freedom of Information Act request shed new light on a little-noticed and expanding network of surveillance for which there appear to be few legal limitations.

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ICE’s use of some of the information in states including California also appears to skirt limitations that so-called sanctuary cities have placed on police cooperation with the immigration agency, the ACLU said.

“The ACLU’s grave concerns about the civil liberties risks of license plate readers take on greater urgency as this surveillance information fuels ICE’s deportation machine,” wrote Vasudha Talla, a staff attorney with the ACLU of Northern California, in a blog post.

Talla said the “information is stored for years, generating a literal and intimate roadmap of people’s private lives,” and stressed the data show that cities and states need to adopt tougher rules governing when, and how, license-plate scans should be used.

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ICE did not immediately respond to a request for comment. Spokespeople for the police departments in Austin and Union City, California, also did not immediately respond to requests.

Mounted on police squad cars and above major roads, the scanners automatically log the time, location and license plate of all the cars that pass by, filling out a database that law-enforcement authorities could use to precisely monitor a person’s travels, according to the ACLU.

The database contains years of data about many of the cars on American roads and tracks not only traffic violators, but practically any car that passed a bridge, tow truck or parking garage where the cameras were in use.

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That’s become a valuable trove for ICE, which has been able to access driver-location information culled from businesses in America’s 50 biggest metropolitan areas, the ACLU records show. Thousands of ICE employees, including some who work on deportation cases, have access to the database, the watchdog group said.

ICE agents also appeared to have access to data voluntarily shared by dozens of local police agencies across the U.S., even in places that have policies limiting police cooperation with ICE. More than 80 local law-enforcement agencies across California, Texas and other states that also use the system appear to have chosen to make their data available to ICE, according to a report unearthed by the ACLU.

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Among them appear to be so-called “sanctuary cities” that generally refuse to help with federal deportation efforts, such as Union City, California, according to a report included in the documents. The ACLU said it is unclear if local residents had been aware of the relationship, but argued it amounted to a violation of state law, which prohibits California police agencies from cooperating with ICE.

Also on the list is the Austin Police Department, where lawmakers have instituted restrictions on officers’ coordination with ICE. In other cases, emails unearthed by the ACLU show ICE agents asking seemingly friendly local law-enforcement officials for access to license-plate data they may not have been able to see otherwise.

ICE signed a $6 million contract in 2017 that gave it access to data maintained by Vigilant Solutions, a California-based security-technology company. The agency announced at the time that it would use it to support “criminal and administrative law enforcement missions.”

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Some ICE field agents had been using such a system for years, despite longtime objections from consumer-protection advocates and lawmakers in Congress. The Department of Homeland Security itself had scrapped a plan in 2014 to develop a national license-plate tracking database in response to privacy concerns.

Vigilant says its database has more than 5 billion nationwide license-plate “detections” and adds another 150 million more every month. Officers can search for a license plate to find everywhere that car was seen on camera, or get alerted whenever the license plate is spotted.

The documents include emails in which ICE agents asked police officers to hand over driver information from the database to help investigate specific targets. ICE’s privacy rules say that license-plate data searches may be used for authorized criminal law-enforcement purposes, including removing “criminal aliens, fugitive aliens (and) illegal reentrants.”

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Critics say the system subjects innocent people to an improper level of government surveillance, because the scanners log license-plate data on every passing car, and not just those owned by criminal suspects. Unlike the GPS-tracking devices that police must get warrants to legally use, officers can access years of data without getting permission from a judge.

“ICE has long embraced technology to target immigrants,” the ACLU’s Talla said. “Now it’s taking surveillance to an unprecedented level to target vulnerable communities – and sweeping up everyone else in the process.”