When Sergeant Lee DeBrabander marked a case confidential in the Long Beach drug squad’s Palantir data analysis system in November 2014, he expected key details to remain hidden from unauthorized users’ eyes. In police work, this can be crucial—a matter of life and death, even. It often involves protecting vulnerable witnesses, keeping upcoming operations hush hush, or protecting a fellow police officer who’s working undercover.

Yet not long after, someone working in the gang crimes division ran a car license plate mentioned in his case and was able to read the entire file. “Can you please look at this?” DeBrabander wrote to a Palantir engineer in an email, which was obtained by Backchannel in response to public records requests.

Mark Harris is a freelance journalist reporting on technology from Seattle. Sign up to get Backchannel's weekly newsletter.

Palantir had been selling its data storage, analysis, and collaboration software to police departments nationwide on the basis of rock-solid security. “Palantir Law Enforcement provides robust, built-in privacy and civil liberties protections, including granular access controls and advanced data retention capabilities,” its website reads.

But DeBrabander had a hard time getting Palantir to respond, emails show. Two weeks after he made his first complaint, his sensitive case was still an open book to other detectives at Long Beach PD. “I went over to Gangs and had them run the plate since they are not listed in our confidentiality group, and sure enough the plate was found within the narrative of the very report we want to keep tight control on,” he complained in an email to Palantir. Four months later, his case was still visible to other officers, and he was still sending emails to Palantir to fix the problem.

Law enforcement accounts for just a small part of Palantir’s business, which mostly consists of military clients, intelligence outfits like the CIA or Homeland Security, and large financial institutions. In police departments, Palantir’s tools are now being used to flag traffic scofflaws, parole violators, and other everyday infractions. But the police departments that deploy Palantir are also dependent upon it for some of their most sensitive work. Palantir’s software can ingest and sift through millions of digital records across multiple jurisdictions, spotting links and sharing data to make or break cases.

The scale of Palantir’s implementation, the type, quantity and persistence of the data it processes, and the unprecedented access that many thousands of people have to that data all raise significant concerns about privacy, equity, racial justice, and civil rights. But until now, we haven’t known very much about how the system works, who is using it, and what their problems are. And neither Palantir nor many of the police departments that use it are willing to talk about it.

In one of the largest systematic investigations of the company to date, Backchannel filed dozens of public records requests with police forces across America. When Palantir started selling its products to law enforcement, it also laid a paper trail. All 50 states have public records laws providing access to contracts, documents, and emails of local and government bodies. That makes it possible to peer inside the company’s police-related operations in ways that simply aren’t possible with its national security work.