Chairman Bennie Thompson, D-Miss., gaveled in the hearing just after 1:00 p.m. on Thursday.

In his opening statement, Thompson once again outlined what the committee called a "multi-part plan" by Trump to contest his election loss -- one Thompson said has come into focus in large part because of witness testimony.

"The most striking fact is that all this evidence comes almost entirely from Republicans," Thompson said. "The evidence that has emerged did not come from Democrats or opponents of Donald Trump."

Thompson continued, "Instead, look at who's written and testified and produced evidence. Who has that been? Aides who've worked loyally for Trump for years, Republican state officials and legislatures, Republican electors, the chairwoman of the Republican National Committee."

Bombshell testimonials so far have come from former Attorney General Bill Barr, former White House aide Cassidy Hutchinson, Ivanka Trump, Jared Kushner and others.

Thompson said the committee Thursday will play new testimony from additional Republicans that served in the Trump administration, as well as never-before-seen footage of congressional leaders on Jan. 6.

Chairman Bennie Thompson, D-Miss., told ABC News ahead of the hearing that the committee hasn't ruled out issuing a subpoena to Trump.

The panel has yet to ask Trump for his testimony, but has centered their hearings on what they described as his “sophisticated” plan to carry out an attempted coup.

Thompson also said that "there's always a possibility" the committee asks for former Vice President Mike Pence's testimony. But then Thompson said that after this hearing, the committee is unlikely to call any new witnesses they haven't already spoken with.

--ABC News’ Katherine Faulders and Will Steakin

Committee aides, during a background call with reporters on Wednesday, wouldn't shed any light on whether and when they would call Trump or former Vice President Mike Pence to formally testify before the panel before their investigation is wrapped.

Pence this summer said he would "consider" testifying if invited by the committee but expressed constitutional concerns about such a scenario, citing his "unique role" as the then-vice president.

Vice chair Liz Cheney, R-Wyo., told ABC News' Jonathan Karl in August that she hopes Pence will appear before the committee but declined to weigh in on whether they would ask Trump to testify.

"I don't want to get in front of committee deliberations about that," Cheney said. "I do think it's very important, as I said in the first hearing or the second hearing, you know, his interactions with our committee will be under oath."

--ABC News' Katherine Faulders

Lawmakers will focus on Trump's "state of mind" leading up to, during and after the insurrection during Thursday's session, committee aides told reporters.

"What you're going to see is a synthesis of some evidence we've already presented with that new, never-before-seen information to, let's say, illustrate Donald Trump's centrality from the time prior to the election," an aide said.

While there won't be any live witnesses in the hearing room, the panel's expected to air new documentary evidence and video footage depicting efforts to respond as the violence broke out on Jan. 6, 2021.

The hearing is expected to kick off at 1 p.m.