(CNN) Matthew Pottinger, who served on former President Donald Trump's National Security Council before resigning in the immediate aftermath of January 6, 2021, will testify publicly at Thursday's prime-time hearing held by the House select committee investigating the US Capitol attack, according to multiple sources familiar with the plans.
Pottinger is slated to appear alongside former Trump White House aide Sarah Matthews.
CNN previously reported that Matthews, who served as deputy press secretary in the Trump White House until resigning shortly after January 6, 2021, was expected to testify publicly. When she resigned, Matthews said she was honored to serve in Trump's administration but "was deeply disturbed by what I saw." She said at the time, "Our nation needs a peaceful transfer of power."
Pottinger, Trump's deputy national security adviser, stepped down in response to Trump's reaction to his supporters breaching the US Capitol, a person close to Pottinger confirmed to CNN at the time of his resignation. He told people there was very little for him to consider, the person said at the time.
The committee's vice chairwoman, Republican Rep. Liz Cheney of Wyoming, described Pottinger like this during one of the committee's previous hearings: "A former Marine intelligence officer who served in the White House for four years, including -- including as deputy national security adviser, was in the vicinity of the Oval Office at various points throughout the day."
The committee played a video clip from Pottinger's interview in which he described the moment he knew it was the moment to resign.
"One of my staff brought me a printout of a tweet by the President, and the tweet said something to the effect that Mike Pence, the vice president, didn't have the courage to do what he -- what should have been done. I -- I read that tweet and made a decision at that moment to resign. That's where I knew that I was leaving that day once I read that tweet."
A spokesperson for the committee declined to comment. A spokesperson for Pottinger did not respond to CNN's request for comment.
The public has now heard live testimony from more than a dozen witnesses and seen clips from the recorded depositions of more than 40 others, including members of the Trump family, former administration officials, GOP officials from key battleground states, and members of the former President's legal team.
Thursday's hearing will mark the panel's second prime-time session, and committee members have said it will examine Trump's inaction for 187 minutes while the US Capitol riot was unfolding.
Democratic Rep. Elaine Luria of Virginia, who will be leading Thursday's hearing with GOP Rep. Adam Kinzinger of Illinois, told CNN the committee will "go through pretty much minute by minute" the then-President's actions.
"He was doing nothing to actually stop the riot," the Virginia Democrat told CNN's Dana Bash on "State of the Union."
One person not expected to attend Thursday's hearing in person is the committee's chairman, Democratic Rep. Bennie Thompson of Mississippi. Thompson announced Tuesday that he tested positive for Covid-19 and would isolate in the coming days. A committee spokesman said Thursday's hearing would not be affected.
On Tuesday, the committee met with former Trump White House aide Garrett Ziegler, a former aide to then-White House economic adviser Peter Navarro, who may be able to provide the committee with additional information about the circumstances around a heated Oval Office meeting on December 18, 2020. During that 2020 meeting, White House lawyers clashed with outside Trump allies regarding their extreme proposals for how to overturn the 2020 presidential election. CNN has previously reported that seizing voting machines and appointing a special counsel to investigate baseless claims of widespread election fraud were discussed.
This headline and story have been updated with additional reporting.