Two legal activist groups have lost their appeal in a public records lawsuit filed against the Los Angeles Police Department and the Los Angeles Sheriff’s Department regarding license plate reader (LPR) data.

The Electronic Frontier Foundation (EFF) and the American Civil Liberties Union of Southern California (ACLU SoCal) had sued those law enforcement agencies to gain access to one week’s worth of LPR data as a way to better understand this surveillance technology. After losing in Los Angeles Superior Court last August, the EFF and ACLU SoCal appealed; the court’s decision was handed down on Wednesday.

Both agencies, like many others nationwide, use these specialized cameras to scan cars and compare them at incredible speeds to a "hot list" of stolen or wanted vehicles. In some cases, that data is kept for weeks, months, or even years. Handing over such a large volume of records by a California law enforcement agency is not without precedent.

Earlier this year, Ars obtained 4.6 million LPR records collected by the police in Oakland over four years and learned that just 0.16 percent of those reads were "hits." We discovered that such data is incredibly revelatory—we were even able to find the city block where a member of the city council lives, using nothing but the database, a related data visualization tool, and his license plate number.

The judge in the initial court ruling found that the law enforcement agencies could withhold LPR records—which include a plate number, date, time, and GPS location—through a particular exemption under the California Public Records Act that allows investigatory records to be kept private. The Court of Appeal of the State of California, Second Appellate District, Division Three agreed:

Contrary to Petitioners’ premise, the plate scans performed by the ALPR system are precipitated by specific criminal investigations—namely, the investigations that produced the “hot list” of license plate numbers associated with suspected crimes. As Real Parties’ experts both testified, the ALPR system’s principal purpose is to check license plates against the hot list to determine whether a vehicle is connected to a crime under investigation. In this way, the ALPR system replicates, albeit on a vastly larger scale, a type of investigation that officers routinely perform manually by visually reading a license plate and entering the plate number into a computer to determine whether a subject vehicle might be stolen or otherwise associated with a crime.

The judges also noted that the scope of the amount of data collected under the LPR system is “apart” from cases that had been addressed by other California courts, but they concluded that such a distinction was “irrelevant” to whether or not such records constituted an investigation.

“We are obviously disappointed with the ruling and believe it sets a very bad precedent for public access to law enforcement records,” Jennifer Lynch , an attorney with the EFF, told Ars by e-mail. “Although more than 99 percent of the millions of ALPR records collected on drivers in Los Angeles every week are never linked to any criminal or vehicle investigation, the California Court of Appeal held LAPD and LA Sheriff’s Department could withhold them as ‘investigative records.’"

"But based on this interpretation of the California Public Records Act (PRA), other important information like body camera footage would also be exempt," Lynch said. "This means Californians would never be able to use the PRA to find out what information law enforcement agencies are collecting on us or even to get access to footage that could show how law enforcement officers are interacting with the public during protests like the ones that recently occurred in Baltimore. We are currently considering our options, including a petition to the California Supreme Court for review.”

Neither the LASD nor the LAPD have previously responded to Ars’ request for comment on this case.