Disgraced FBI official Peter Strzok testified for hours behind closed doors on Capitol Hill Wednesday, following the revelations of numerous anti-Trump messages he exchanged with a bureau colleague and lover during the 2016 presidential campaign.

Those messages, between Strzok and former FBI attorney Lisa Page, included one revealed in the new Justice Department inspector general's report in which Strzok vowed to "stop" Donald Trump from becoming president.

Strzok was questioned for hours before the House Judiciary Committee on Wednesday. Members of the committee sat in for a confidential briefing with Strzok, firing off questions about the start of the Russia investigation and questions on the Clinton email investigation.

“There are still a lot of unanswered questions on who knew what when,” House Freedom Caucus Chairman Mark Meadows, R-N.C., told reporters on the Hill during a break from the hearing. “And as it related to this particular investigation, what was the genesis of the Russia collusion investigation?”

Meadows said that “new information has come out,” but did not share specifics. While it is unclear what specifically was learned in the confidential hearing, a congressional source told Fox News that most GOP members have focused on the Russia investigation and how Strzok relates to the beginning of that probe.

Strzok, 48, appeared before the committee voluntarily, despite being issued a subpoena on Sunday.

Strzok said over the weekend that he was willing to testify before Congress without an immunity deal and that he would not invoke his Fifth Amendment protection against self-incrimination. But because he could not agree to a specific date, the committee issued him a subpoena to appear on Capitol Hill Wednesday.

Fox News learned Tuesday that the subpoena was no longer valid because Strzok voluntarily agreed to appear for the interview.

Sources on the Hill told Fox News that the force of a subpoena was not necessary and that the committee plans to bring Strzok back in the near future for public testimony, something the president said was necessary.

Strzok, who was escorted from his FBI office last week, has been under scrutiny for months over a series of politically-charged text messages exchanged with Page, who left the bureau in May.

Strzok, who was assigned to Special Counsel Robert Mueller's investigation of Russian election meddling, was removed from that team in 2017, following revelations of his anti-Trump text messages.

But earlier this month, Justice Department Inspector General Michael Horowitz revealed a new text message, in which Strzok had vowed to "stop" Trump from becoming president -- and made clear that as many as five FBI employees exchanged politically charged messages.

The inspector general’s report noted that it was specifically concerned about text messages exchanged between FBI officials Strzok and Page that “potentially indicated or created the appearance that investigative decisions were impacted by bias or improper considerations.”

“I don’t know how any reasonable person reads the texts and would suggest there was no bias,” Meadows told reporters. “None of my concerns about political bias have been alleviated based on what I’ve heard so far.”

But Horowitz ultimately found no evidence that the anti-Trump bias among the several FBI agents impacted prosecutorial decisions in the Clinton email probe.

“The only reason they concluded there was not bias in the IG report is because there were multiple people in the decision making process,” Meadows said. “To suggest that Peter Strzok was not biased does not actually correspond with the decisions the IG made.”

Horowitz last week confirmed that he is investigating whether Strzok’s anti-Trump bias factored into the launch of the FBI’s Russia investigation.

Strzok and Page both served for a short period of time on Mueller’s team. Strzok was reassigned following the revelations of his anti-Trump texts.

During testimony on Capitol Hill Tuesday, Horowitz acknowledged that Strzok’s text messages “clearly shows a biased state of mind.”

It was revealed earlier this year that Horowitz’s office was investigating allegations of government surveillance abuse tied to the start of the Russia probe. But Horowitz’s testimony last week, meant to answer questions about the conclusion of the Clinton case review, revealed some of the specifics involved in the ongoing Russia case review, including the Strzok texts.

“I can’t imagine FBI agents even suggesting that they would use their powers to investigate any candidate for office,” Horowitz said last week. “I thought this was completely antithetical to the core values of the department and extremely serious.”

Fox News' Chad Pergram and Paulina Dedaj contributed to this report.