Washington (CNN) The intelligence community inspector general provided documents to the House Intelligence Committee showing how he attempted to corroborate a whistleblower complaint alleging President Donald Trump solicited foreign interference to dig up dirt on Joe Biden, according to two sources familiar with the matter.

Intelligence community inspector general Michael Atkinson briefed the House Intelligence panel behind closed doors today about the whistleblower complaint, two weeks after he appeared before the same committee prior to the complaint being released.

The sources added that Atkinson's testimony mostly covered the process of corroborating the complaint.

A House Intelligence spokesman declined to comment.

Atkinson briefed the committee amid the House Democrats' impeachment inquiry into President Donald Trump and Ukraine, which is focused on the whistleblower complaint he corroborated.

Atkinson is widely regarded as a career non-partisan with little interest in the public limelight, but currently finds himself at the center of the high profile controversy over the whistleblower complaint alleging that the President pressured the Ukrainian president in an effort to "solicit interference" in the 2020 presidential election. The complaint has divided Washington and become the focal point of the impeachment inquiry into the President by House Democrats.

Meanwhile, a Republican aide tells CNN members will ask more about how the complaint was drafted and if others were involved. They also want to know how the inspector general deemed it credible and what the perceived potential political bias was -- an indication that they plan to go after the credibility of the complaint itself.

Michael Atkinson, Inspector General of the Intelligence Community

This won't be Atkinson's first visit to the Hill as the controversy over the President and his actions with respect to Ukraine has unfolded. Last week, Atkinson appeared behind closed doors with the Senate Intelligence Committee. He also appeared before the House Intelligence Committee two weeks ago, but that was before the whistleblower complaint had been released, which is why the committee is calling him back Friday.

Rep. Mike Quigley, an Illinois Democrat on the committee, told reporters as he left the briefing that Atkinson "cemented" how "thorough he was" in corroborating the complaint. Quigley declined to provide details about how the inspector general corroborated the complaint.

"Let's put this in perspective, folks," he said. "What the inspector general said last time was the whistleblower pulled the fire alarm. We have now seen the smoke and the fire."

Republicans left the briefing saying that the inspector general did not provide any information about the contact the whistleblower had with a Democratic aide on the House Intelligence Committee before the complaint was filed.

"I can tell you one thing that we've learned very clearly, and that is that the IG for the Intelligence Community can provide no information about the contacts between the HPSCI majority, and the whistleblower prior to his involvement," said Rep. John Ratcliffe, a Texas Republican on the panel, arguing that the contact between the committee and the whistleblower disqualified House Intelligence Chairman Adam Schiff from running the committee's investigation into the complaint.

Friday's briefing with the inspector general is the latest indication House Democrats are attempting to move swiftly in their investigation, which has continued despite the fact that the House is currently in a two-week recess period.

Schiff, a California Democrat, announced that Atkinson would appear before the panel in a "Dear Colleague" letter last week updating lawmakers on the next steps in the ongoing investigation.

"The House Intelligence Committee will hold a closed briefing with the Inspector General of the Intelligence Community on Friday, October 4," Schiff wrote, adding, "The IC IG conducted a preliminary investigation and determined that the whistleblower complaint was credible. This hearing is critical to establish additional details, leads and evidence."

Congressional Democrats have argued that the Ukraine matter is a betrayal of the President's oath of office, but many congressional Republicans have instead turned to attacking the credibility of the whistleblower, arguing that the account amounts to "hearsay," though a transcript provided by the White House backs up some of the allegations outlined in the whistleblower's complaint.

The office of the Intelligence Community inspector general forcefully also pushed back on Republicans' argument in a rare statement on Monday, saying, "The whistleblower stated on the form that he or she possessed both first-hand and other information."

"The ICIG reviewed the information provided as well as other information gathered and determined that the complaint was both urgent and that it appeared credible," the statement read.

This story has been updated with additional developments Friday.