Google “systematically destroyed” instant message chats every 24 hours, violating federal rules to preserve potentially relevant communications for litigation, the Department of Justice alleged in a filing that became public on Thursday.

As a result of Google’s default to preserve chats for only 24 hours unless an employee opts to turn on history for the conversation, “for nearly four years, Google systematically destroyed an entire category of written communications every 24 hours,” the department wrote in the filing.

According to the DOJ, Google should have adjusted its defaults in mid-2019 “when the company reasonably anticipated this litigation.” Instead, it relied on individual employees to decide when chats were potentially relevant to future litigation, the department said.

“Few, if any,” did, according to DOJ.

Meanwhile, investigators alleged, Google “falsely” told the government it had “‘put a legal hold in place’ that ‘suspends auto-deletion.'” The government added that “at every turn, Google reaffirmed that it was preserving and searching all potentially relevant written communications.”

The data deletion continued up until as recently as this month when the government indicated it would file a motion for sanctions and an evidentiary hearing, investigators allege. At that point, the DOJ said, Google committed to “permanently set to history on.”

A Google spokesperson said in a statement company officials “strongly refute the DOJ’s claims. Our teams have conscientiously worked for years to respond to inquiries and litigation. In fact, we have produced over 4 million documents in this case alone, and millions more to regulators around the world.”

The alleged issue is one that previously came up in Epic Games’ antitrust litigation against Google.

Epic submitted exhibits in that case that seemed to show some Google employees believed chats were a safer place to conduct sensitive conversations. For example, one exhibit shows an employee comment on a document that says “Since it’s a sensitive topic, I prefer to discuss offline or over hangout,” referring to Google’s chat product.

The parties in that suit hashed out the issue in front of a federal judge in the Northern District of California this year in two evidentiary hearings.

At one of those hearings on Jan. 31, Judge James Donato indicated he would be open to a kind of adverse jury instruction, but one that would allow the jury to draw its own conclusions on what the deletion of messages means for the case.

An adverse jury instruction, in its most stringent form, would instruct a jury that it should assume that the relevant documents that were destroyed would have cast Google in a negative light, according to Eileen Scallen, a professor at the UCLA School of Law, an expert in evidence and civil procedure. A lesser remedy could be to instruct the jury to not hold it against the plaintiff for not having specific documents to back up its claims.

Donato telegraphed that he might issue an instruction that falls somewhere in between, stressing his language was subject to change. He said such an instruction may be something along the lines of telling the jury that if it finds Google didn’t adequately preserve some documents, it may conclude those documents were adverse to the company’s interests.

While it’s difficult to replace the value of documents that could have become important evidence, Scallen said an adverse jury instruction is considered “very damning.”

“The one person the jury respects in a courtroom is the trial judge,” Scallen said in a phone interview late last month regarding the Epic case. “And if the trial judge is telling them you can presume that this was bad news for Google, they’re going to take that to heart.”

The DOJ alleged that even after Epic confronted Google about the chat-deletion concerns in that case, the tech giant still withheld its deletion policy from the federal government “and continued to destroy written communications in this case.”

The practices denied the federal prosecutors the chance to view “candid discussions between Google’s executives, including likely trial witnesses,” the government claimed.

The Justice Department is asking that the court hold that Google violated a federal rule of civil procedure by destroying the chats, order a hearing to figure out how to sanction the company and remedy the alleged destruction of evidence and order it to provide more information about its chat practices.

Scallen said that if Google “didn’t give clear directions to retain” relevant chats “this notion that they left it to the individuals, that’s just not responsible.”

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