Two activist groups have filed an appeal in their lawsuit against the Los Angeles Police Department and the Los Angeles Sheriff’s Department to access one week’s worth of license plate reader data. The Electronic Frontier Foundation (EFF) and the American Civil Liberties Union of Southern California (ACLU SoCal) lost their case before a Los Angeles Superior Court judge last month.

In May 2013, the American Civil Liberties Union of Southern California and the Electronic Frontier Foundation sued the law enforcement agencies in an attempt to compel the agencies to release a week’s worth of LPR data from a particular week in August 2012.

The judge in the lower court ruling found that the law enforcement agencies could withhold such license plate reader (LPR) records through a particular exemption under the California Public Records Act that allows investigatory records to be kept private.

In their Tuesday court filing, the groups argued to the appellate court that such a finding "demonstrates a fundamental misunderstanding of how the technology operates and of Petitioners’ purpose in seeking these records."

They continued, "Second, based in part on its misunderstanding of the technology, the Superior Court held that ALPR data—collected indiscriminately on all Los Angeles drivers—constitutes 'records of . . . investigations' under § 6254(f). This holding means that all vehicles on the streets of Los Angeles are constantly under investigation, a conclusion that simply does not fit with common understanding of the term 'investigation,' and which inappropriately expands the scope of § 6254(f) beyond all precedent."

In late July 2012, the ACLU and its affiliates sent requests to local police departments and state agencies across 38 states to request information on how LPRs are used.

LAPD has 242 car-mounted cameras

As Ars has previously reported, LPRs are used in cities big and small across the United States. Typically, the specialized cameras scan a given plate using optical character recognition technology, checking that plate against a "hot list" of stolen or wanted vehicles. The device typically records the date, time, and GPS location of any plate that it sees.

The cameras scan at an extremely high rate, usually around 60 plates per second. Law enforcement policies vary widely concerning how long that information can be retained. Different agencies keep that data anywhere from a few weeks to indefinitely. Some cities have even mounted such cameras at their city borders, monitoring who comes in and out. Various jurisdictions disagree about whether individuals can access their own LPR records, much less a broader dataset.

In December 2013, the Boston Police Department (BPD) indefinitely halted its use of LPRs following an investigation into their use by the investigative journalism organization MuckRock and the Boston Globe.

The LAPD declared in court that it began testing LPRs in 2004, and it currently has 242 such equipped patrol cars as well as 32 fixed-location cameras. The agency argued that if it was compelled to turn over raw LPR data, "its value as an investigative tool would be severely compromised." Police lawyers argued that a criminal could potentially request information about themselves, "thereby learning whether LAPD has evidence regarding his or her whereabout on a particular date and time or near a particular location. This could result in the potential destruction of evidence."

The court largely agreed with police reasoning, finding that an exemption to the California Public Records Act under Section 6254(f), which protects investigatory files, was warranted.

"The hot list comparisons and targeted mobile car patrol inquiries are just such records of investigation," Los Angeles Superior Court Judge James C. Chalfant wrote in his August 2014 decision. "Law enforcement is conducting these investigations looking for stolen cars and other evidence of crime. While it is less clear that ALPR data from fixed point and random mobile car patrol cameras are records of investigation, the broad nature of the exemption for law enforcement investigatory records requires their inclusion."