In a combative exchange at a hearing Friday in Washington, D.C., a federal judge unabashedly accused career State Department officials of lying and signing "clearly false" affidavits to derail a series of lawsuits seeking information about former Secretary of State Hillary Clinton's private email server and her handling of the 2012 terrorist attack on the U.S. Consulate in Benghazi, Libya.

U.S. District Court Judge Royce Lamberth also said he was "shocked" and "dumbfounded" when he learned that FBI had granted immunity to former Clinton chief of staff Cheryl Mills during its investigation into the use of Clinton's server, according to a court transcript of his remarks.

"I had myself found that Cheryl Mills had committed perjury and lied under oath in a published opinion I had issued in a Judicial Watch case where I found her unworthy of belief, and I was quite shocked to find out she had been given immunity in — by the Justice Department in the Hillary Clinton email case," Lamberth said during the hearing.

The Department of Justice's Inspector General (IG), Michael Horowitz, noted in a bombshell report in June that it was "inconsistent with typical investigative strategy" for the FBI to allow Mills to sit in during the agency's interview of Clinton during the email probe, given that classified information traveled through Mills' personal email account. "[T]here are serious potential ramifications when one witness attends another witness' interview," the IG wrote.

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Lamberth, who was appointed to the bench by President Ronald Reagan, said he did not know Mills had been granted immunity until he "read the IG report and learned that and that she had accompanied [Clinton] to her interview."

"I was actually dumbfounded when I found out ... that Cheryl Mills had been given immunity." — U.S. District Court Judge Royce Lamberth

The transparency group Judicial Watch initially sued the State Department in 2014, seeking information about the response to the Benghazi attack after the government didn't respond to a Freedom of Information Act (FOIA) request. Other parallel lawsuits by Judicial Watch are probing issues like Clinton's server, whose existence was revealed during the course of the litigation.

The State Department had immediately moved to dismiss Judicial Watch's first lawsuit on a motion for summary judgment, saying in an affidavit that it had conducted a search of all potentially relevant emails in its possession and provided them. The affidavit noted that some more documents and emails could be forthcoming.

But Lamberth denied the request to dismiss the lawsuit at the time -- and on Friday, he said he was happy he did, charging that State Department officials had intentionally misled him because other key documents, including those on Clinton's email server, had not in fact been produced.

"It was clear to me that at the time that I ruled initially, that false statements were made to me by career State Department officials, and it became more clear through discovery that the information that I was provided was clearly false regarding the adequacy of the search and this – what we now know turned out to be the Secretary’s email system," Lamberth said Friday.

He continued: "I don’t know the details of what kind of IG inquiry there was into why these career officials at the State Department would have filed false affidavits with me. I don’t know the details of why the Justice Department lawyers did not know false affidavits were being filed with me, but I was very relieved that I did not accept them and that I allowed limited discovery into what had happened."

During a tense exchange with Justice Department lawyer Robert Prince, Lamberth pressed the issue, accusing Prince of using "doublespeak" and "playing the same word games [Clinton] played."

That "was not true," the judge said, referring to the State Department's assurances in a sworn declaration that it had searched all relevant documents. "It was a lie."

But Prince pushed back sharply, saying he took the judge's accusations "extremely seriously."

"It might be that our search could be found to be inadequate, but that declaration was absolutely true," he said.

"Now, it's been made clear in rulings by various courts that, basically, the courts are going to expect us to search items that come in afterward in this instance, and that's understandable, but at the time, that was not at all clear, you know?" Prince continued. "I understand if Your Honor thinks that the searches that were done up to the motion for summary judgment were inadequate, but being wrong about the search being adequate does not make it a false affidavit."

"It's true that we told Judicial Watch ... State was done when it was not done." — Justice Department lawyer Robert Prince

He added: "And as far as bad faith goes, it's true that we told Judicial Watch we were done -- State was done when it was not done, but what it did on its own was conduct that search. So it's not -- it's hard to say that's bad faith. We found out -- we got the emails and searched them. That's what's supposed to happen in a FOIA case. Now, ideally in the FOIA case, those records would have been at State. Of course, not having those records made some FOIA cases not be resolved correctly or made -- it obstructed FOIA. We're not arguing that."

Lamberth ultimately conceded that he had "misremembered" some details on the issue, although he didn't back off his claims that the government had been intentionally deceptive.

An attorney for Judicial Watch then told Lamberth that the State Department didn't provide the court information about Clinton's email server in status report documents filed just one month before The New York Times publicly revealed the server's existence. Prince responded that it was "normal FOIA practice to not disclose that kind of information in such a status report."

In a statement, Judicial Watch President Tom Fitton, who was present at the hearing, pushed the White House for answers.

“President Trump should ask why his State Department is still refusing to answer basic questions about the Clinton email scandal,” Fitton said. “Hillary Clinton’s and the State Department’s email cover up abused the FOIA, the courts, and the American people’s right to know.”

The hearing was held because Judicial Watch is seeking to compel Clinton and other officials to testify and provide more information as part of its lawsuit.

Clinton has since blamed Republicans and groups like Judicial Watch for derailing her presidential bid in 2016.

“Take the Benghazi tragedy—you know, I have one of the top Republicans, Kevin McCarthy, admitting we’re going to take that tragedy—because, you know, we’ve lost people, unfortunately, going back to the Reagan administration, if you talk about recent times, in diplomatic attacks,” Clinton said on NBC’s “Today" in an interview last year. “But boy, it was turned into a political football. And it was aimed at undermining my credibility, my record, my accomplishments.”

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Four Americans were killed in the attack on the Benghazi embassy, and the Clinton State Department was faulted for ignoring security concerns in the run-up to the attack, contributing to the poor defense posture at the post.

The independent government Accountability Review Board that examined the tragedy concluded there were “systemic failures and leadership and management deficiencies at senior levels” at the department that “resulted in a Special Mission security posture that was inadequate for Benghazi and grossly inadequate to deal with the attack that took place.”

Then-national security adviser Susan Rice claimed on several talk shows that the attack was caused by a YouTube video, even as e-mails uncovered after the fact revealed that administration officials knew the incident was the result of terrorism. Officials at the State Department were stunned by Rice's appearances, according to the emails, with one State Department employee suggesting Rice had gone "off the reservation."

Rice has since openly suggested she is considering running against Maine moderate Republican Sen. Susan Collins because of her vote to support Supreme Court Associate Justice Brett Kavanaugh's confirmation. Rice called Collins' speech announcing her vote a "paean to disingenuousness and incoherence."

But Collins has downplayed any potential challenge from Rice.

"As far as Susan Rice is concerned, her family has a home in Maine, but she doesn’t live in the state of Maine," Collins said earlier this month. "Everybody knows that."

Fox News' Brooke Singman contributed to this report.