The LAPD has not said how many ALPR cameras it owns or has access to, although documents show that it shares images with cameras from the Los Angeles Sheriff’s Department, Long Beach, Glendale, and Burbank police, as well as with Burbank, LAX, and Van Nuys airports. It has also used images from civilian ALPR cameras, typically deployed in shopping malls, universities, and transit centers for security.

ALPR systems are now widely used by law enforcement in the US and around the world. Surveys collected by the federal Bureau of Justice Statistics in 2013 found that 93 percent of police departments in cities with 1 million or more people used ALPR. Even half the departments serving towns as small as 25,000 people have ALPR. One ALPR company, Vigilant Solutions, claims that it carries out over a billion license plate scans each year.

Such systems traditionally have been used by law enforcement to help locate stolen vehicles. But when ALPR data is stored for years and then integrated with analytical systems like Palantir, it becomes much more powerful—and potentially open to abuse.

According to a Palantir user guide for the LAPD disclosed to WIRED, detectives start by logging in with their police credentials. When the system launched in 2009, officers had to type in why they were searching. Many would just enter “investigation” or the numeric code for a crime, like “459” for burglary, according to a 2014 email to users from John Gaw, a sheriff’s department sergeant responsible for working with Palantir.

Gaw warned Palantir users to better justify requests for ALPR searches, lest the department attract more attention from civil liberties groups. “[We] are facing potential limitations on the use … of the ALPR database by the ACLU,” he wrote. “We may be challenged to … show we are … making sure every user has a valid reason.”

Officers misusing law enforcement databases for their own purposes is a perennial problem at the LAPD and elsewhere. Some officers weren’t happy about Gaw’s team auditing ALPR requests and questioning vague rationales. “Unfortunately they have been contacting every user that puts in an unacceptable search reason,” wrote another LASD sergeant, Peter Jackson.

Searching by Plate Number, or by Area

In its latest version that went live in May 2016, called ALPR 2.0 or TBird, Palantir’s ALPR system requires users to enter a specific case number, and to select a purpose for each search via a pulldown menu. However, some of the reasons are vague, such as “protect critical infrastructure” or “protect the public during events.”

“The broad language for categorizing searches suggests that no indication of criminality is required to make a query,” says the ACLU’s Bibring. “If that’s the case, it’s basically the Wild West for when officers can query millions of data points.” Neither Palantir nor the LAPD responded to multiple requests for comment on this story.

Once in the system, detectives have several options. If they have a full or partial plate number, they can search using that. The system will then display matching plates, and a map view showing every time each plate was captured by the ALPR system.

A Timeline button brings up a chart showing how many times a plate has been searched, while a Freq Analysis feature displays a table showing those hits by time of day, and day of the week. These can help detectives spot patterns, such as where a vehicle’s driver might live or work.

Palantir’s TBird also works in reverse. Users can draw a circle on a map, then ask for a list of all the license plates spotted in that area at a given time. Sarah Brayne, a sociologist at the University of Texas at Austin who studied data surveillance at the LAPD for several years, detailed how this helped solve the murder of someone dumped at a remote tourist location. A nearby ALPR camera captured three cars around the time the body was dumped. The registered owner of one of the cars was affiliated with a gang then at war with the victim’s gang. Using that information, officers obtained a search warrant, examined the car for evidence, and arrested a suspect.