WASHINGTON — The House January 6 committee plans to extend its public hearings into July as its investigation of the Capitol riot deepens and the Justice Department widens its own look into alternative slates of electors following the 2020 election.

The committee chairman, Representative Bennie Thompson, told reporters Wednesday that the committee is receiving “a lot of information” — including new documentary film footage of President Trump’s final months in office — as its yearlong inquiry intensifies with hearings into the attack on January 6, 2021, and Mr. Trump’s efforts to overturn the 2020 election.

The committee is also working on setting up an interview with the conservative activist and wife of Justice Clarence Thomas, Virginia “Ginni” Thomas, who has responded to the panel’s request to appear, the chairman said. She was asked to speak to the committee after disclosures of her communications with Mr. Trump’s team in the run-up and day of the insurrection at the Capitol.

“It’s our expectation that we will keep talking and trying to get her to come in,” said Mr. Thompson, a Mississippi Democrat.

Mrs. Thomas has previously said she “can’t wait to clear up misconceptions,” suggesting she would comply with the panel’s request to testify.

For the past year, the committee has been investigating the violence at the Capitol and its causes, and has interviewed more than 1,000 witnesses and produced some 140,000 documents. Nine people died in the attack and its aftermath.

The next hearing, set for Thursday, is expected to highlight former Justice Department officials testifying about Mr. Trump’s proposals to reject the election results. It would wrap up this month’s work. The committee would start up again in July, Mr. Thompson said.

The panel has issued a new subpoena for testimony to an Alabama Republican, Representative Mo Brooks, who was among a group of five GOP lawmakers, including the minority leader, Representative Kevin McCarthy, the committee wants to hear from about their interactions with Mr. Trump before or during the Capitol riot, the chairman said.

Mr. Brooks, who was defeated this week in Alabama’s GOP primary for the United States Senate and had lost favor with Mr. Trump, initially indicated he may speak to the panel. But Mr. Thompson said the subpoena had expired, so a new one needed to be sent. Mr. McCarthy and the other Republican lawmakers are declining to appear.

Meanwhile, in a sign of a widening Justice Department investigation, federal law enforcement officials served a round of subpoenas Wednesday related to alternate — or fake — slates of electors who falsely sought to declare Mr. Trump the winner in their states in 2020.

The House committee has already been investigating the matter, but the new subpoenas underscore the Justice Department’s interest in the same area. The recipients of the subpoenas included the chairman of the Georgia Republican Party, David Shafer, according to a person familiar with the matter who insisted on anonymity to discuss an ongoing investigation. The Washington Post was first to report on the subpoenas.

The committee had been scheduled to conclude this first round of public hearings in June. But additional information has come to the committee’s attention, and Congress is set to recess for two weeks of remote and district work into the Fourth of July holiday.

“We have a new documentary from a person that we’re talking to, and we got to look through all his information,” Mr. Thompson said, referring to the British filmmaker whose never-before-seen interviews with the former president and his inner circle were turned over to the committee this week. The footage was taken both before and after the insurrection.

The revelation about the film came to light Tuesday when British filmmaker Alex Holder revealed he had complied with a congressional subpoena to turn over all of the footage he shot in the final weeks of Mr. Trump’s 2020 reelection campaign.

Representative Jamie Raskin, a Maryland Democrat, indicated Tuesday that the investigation’s schedule may be changing.

“I would just say the original hearings would have wrapped up in June, but we are picking up new evidence on a daily basis with enormous velocity,” Mr. Raskin said. “And so we’re constantly incorporating and including the new information that’s coming out.”

He added, “But certainly the hearings will conclude before the end of the summer.”