Former U.S. Attorney for the Southern District of New York Geoffrey Berman is testifying behind closed doors on Capitol Hill Thursday over his firing by Attorney General William Barr last month.

Berman arrived on Capitol Hill Thursday before noon, and is set to testify in private before the House Judiciary Committee as part of its investigation into his removal.

BARR SAID TRUMP FIRED SDNY PROSECUTOR WHO REFUSED TO LEAVE, TRUMP SAYS HE'S 'NOT INVOLVED'

Committee Chairman Jerrold Nadler, D-N.Y., vowed last month that his panel would “immediately open an investigation” into Berman’s ouster.

President Trump apparently fired Berman after he refused to step down, though the president had distanced himself from the process.

“Attorney General Bill Barr told us that Geoffrey Berman of the SDNY had resigned – which was untrue,” Nadler said in a statement last month. “Barr told us that the president asked him to fire Mr. Berman  –which may also be untrue, given that the president says he had nothing to do with the decision.”

Nadler added: “The whole thing smacks of corruption and incompetence, which is what we have come to expect from this president and his attorney general.”

Nadler noted that neither the White House nor the Justice Department offered an explanation for Berman’s removal.

DEMS SEIZE ON US ATTORNEY FIRING TO PURSUE NEW PROBES, HEARINGS

The calls to probe Berman’s ouster come after Barr announced last month that Berman would be stepping down from his post at SDNY. Barr and the White House then announced that the president would nominate Jay Clayton, the current chairman of the Securities and Exchange Commission, to replace him.

But Berman put out a statement saying he learned of his “departure” from Barr’s press release and had no intention of leaving the job.

The following day, Barr informed Berman in a letter that the president had removed him from his post. Barr wrote that he asked Trump to fire Berman after his Friday night statement.

The Southern District has pursued a number of Trump associates, including the president's former personal lawyer and fixer Michael Cohen, who served a prison sentence for lying to Congress and campaign finance crimes. The office has also been investigating Trump lawyer Rudy Giuliani’s business dealings, including whether he failed to register as a foreign agent, people familiar with the probe told The Associated Press.

Berman recused himself from directly overseeing the Cohen investigation for reasons that were never disclosed.

Berman has also overseen the prosecution of two Florida businessmen, Lev Parnas and Igor Fruman, who were associates of Giuliani and tied to the Ukraine impeachment investigation. The men were charged in October with federal campaign finance violations, including hiding the origin of a $325,000 donation to a group supporting Trump’s reelection.

Meanwhile, the House Judiciary Committee is leading an investigation into the “unprecedented politicization” at the DOJ under Barr’s leadership.

Barr accepted an invitation to appear before the committee, and is expected to testify in public for a “general oversight hearing” on July 28, the Justice Department confirmed.

Fox News’ Marisa Schultz, Jake Gibson and The Associated Press contributed to this report.