A license plate reader on a Newport News, Virginia, police car. (AP Photo/Daily Press, Joe Fudge) Joe Fudge

SAN FRANCISCO — Civil liberties advocates scored a win at the California Supreme Court on Thursday with a unanimous ruling that data gathered by police license plate readers are not generally exempt from public disclosure under state law.

The American Civil Liberties Union, the Electronic Frontier Foundation, and various news organizations have sought data collected by automated license plate readers (ALPRs) to raise awareness about how much data is collected by police on innocent civilians. ALPRs record the license plates of passing vehicles and check them against a criminal “hot list” for hits.

Some authorities have cooperated with such records requests. The Oakland Police Department, for example, in 2014 handed over data containing tens of thousands of license plates that had been snapped by its cameras—revealing disproportionate license-plate monitoring in Latino and African-American communities, according to an EFF report.

But authorities in Los Angeles balked at a request for a one-week period of raw ALPR data submitted in 2012 by the ACLU and EFF. The LA Police and Sheriff’s departments subsequently won legal challenges at state trial and appellate courts, which found the data were protected by exemptions for police investigations within the California Public Records Act.

Writing for the California Supreme Court in its opinion handed down Thursday, Justice Ming Chin said the lower courts had interpreted that exemption too broadly.

“[T]he animating concern behind the records of investigations exemption appears to be that a record of investigation reveals (and, thus, might deter) certain choices that should be kept confidential—an informant’s choice to come forward, an investigator’s choice to focus on particular individuals, the choice of certain investigatory methods,” Chin wrote. “Such choices are far less likely to be revealed where, as here, data are collected en masse.”

Chin also wrote that the lower courts’ interpretations would allow the LA authorities to claim the records as exempt even if they had placed only a single license plate on their “hot list” and then scanned “literally every plate in Los Angeles.” He added: “In light of CPRA’s purpose of providing access to information regarding government activities, we doubt that the records of investigations exemption was intended to stretch that far.”

The state high court, however, denied the organizations access to raw license plate data. Instead, it said they must work out at the trial court how to best anonymize the information, in order to avoid jeopardizing the privacy interests of individuals whose plates were captured.

Jennifer Lynch, a senior staff attorney at EFF, said the groups had always envisioned that the data would have to be anonymized in some fashion. How much analysis the organizations will be able to do will depend on how the data ends up being sliced, she said.

“When the public or when any of us hear about this mass data collection, it’s very difficult to grasp what that means on a real-world level,” Lynch added, explaining the motivation behind the records request. “But when you have access to that data and can plot that data on a map … I think that really brings it home to people how personal this information is.”

She added the ruling is significant in no small part because the decisions by the lower courts had led some police departments to become uncooperative with records requests.

Undoubtedly, some authorities will be unhappy with the decision. The California State Sheriffs’ Association, California Police Chiefs’ Association, and California Peace Officers’ Association said in an amicus brief prepared by the Jones & Mayer firm that reversal of the appeals court’s decision would render ALPRs “virtually meaningless” as a law enforcement tool.

“Opening up access to these databases to the public will not only compromise law enforcement investigations, it will also expose otherwise unavailable information associated with vehicle license plate numbers to the public that could pose safety or other risks to unknowing vehicle owners,” they wrote. (All the briefs in the case are available on the EFF’s website here.)

The Los Angeles City Attorney’s Office, which represented the LAPD and Sheriff’s Department in the case, did not immediately respond to an email seeking comment on Thursday.

Adam Marshall, an attorney with the Reporters Committee for Freedom of the Press, said the decision is also important given that law enforcement is making increasing use of other electronic surveillance technologies such as body cameras and “stingrays.” Exempting data gathered by those devices from public disclosure laws would impair “the public’s right to know how law enforcement agencies are doing their job,” he said.

Contact Ben Hancock at bhancock@alm.com. On Twitter: @benghancock.