Donald Trump relentlessly pressured top officials at the justice department to pursue groundless claims of voter fraud in an extraordinary but ultimately unsuccessful effort to cling to power, according to testimony the House committee investigating the January 6 insurrection heard on Thursday.

Three former justice department officials who served during Trump’s final weeks in office, told the committee that the then-president was “adamant” that the election was stolen despite begin told repeatedly that none of the allegations raised about the vote count were credible.

Opening the hearing, the panel’s chair, congressman Bennie Thompson, said the hearing would show that the former president sought to “misuse the justice department as part of his plan to hold on to power”.

“Donald Trump didn’t just want the justice department to investigate,” Thompson said. “He wanted the justice department to help legitimate his lies, to basically call the election corrupt.”

After exhausting his legal options and being rebuffed by state and local elections officials, the panel said a desperate Trump turned to the justice department to declare the election corrupt despite no evidence of mass voter fraud, the nine-member panel will seek to show in their fifth and final hearing of the month.

Testifying from the Cannon Caucus Room on Capitol Hill are Jeffrey Rosen, the former acting attorney general; Richard Donoghue, the former acting deputy attorney general; and Steven Engel, the former assistant attorney general for the office of legal counsel.

In one of the near-daily conversations Trump had with the agency’s leader, Rosen told the president that the Department of Justice “can’t and won’t snap his fingers and change the outcome of an election”.

“I don’t expect you to do that,” Trump snapped back, according to Donoghue, whose handwritten notes of the exchange were displayed on a large screen during the hearing. “Just say the election was corrupt and leave the rest to me and the Republican congressmen.”

At the center of Thursday’s hearing was Jeff Clark, a lower-level official at the department who embraced Trump’s myth of a stolen election. At the urging of Republican congressman Scott Perry of Pennsylvania, Trump contemplated replacing Rosen with Clark, an environmental lawyer by trade.

“What was his only qualification?” congressman Adam Kinzinger, an Illinois Republican and member of the committee who led the questioning, asked rhetorically. “He would do whatever the president wanted him to do, including overthrowing a free and fair democratic election.”

The panel voted unanimously to hold Clark in contempt of Congress after he failed to cooperate with its investigation. He later appeared before the committee but he repeatedly asserted his Fifth Amendment right against self-incrimination.

Just before the hearing began, it was revealed that federal investigators searched Clark’s home earlier this week, according to a person familiar with the matter who was not authorized to speak publicly.

In new testimony from the committee’s taped deposition with Bill Barr, the former attorney general said he thought it was important for the department to investigate – and ultimately disprove – Trump’s false claims of voter fraud. Had it not, Barr said he shuddered to think what might have happened. “I’m not sure we would have had a transition at all.”

In previous clips played by the committee, Barr said he told Trump in no uncertain terms that his claims of election fraud were “bullshit”. At one point during his deposition, Barr burst into laughter as he recounted how absurd some of the theories were, including one purportedly orchestrated by Hugo Chávez, the Venezuelan leader who died in 2013.

The committee is building the case that Trump was at the heart of the sprawling conspiracy that led to the violence on January 6 – a lie that has only metastasized in the months since a pro-Trump mob stormed the Capitol with pipes, bear spray and Confederate flags. Nine people died in the assault and its aftermath.

The public hearings are the culmination of a yearlong investigation into the violence on January 6 and the events that led to it. The committee has interviewed more than 1,000 witnesses and collected more than 140,000 documents. But it continues to amass new evidence.

Thompson told reporters this week that the committee had received “a lot of information”, including documentary footage of Trump’s final months in office. It also plans to speak with Ginni Thomas, the conservative activist and wife of the supreme court justice Clarence Thomas who was in close contact with Trump’s chief of staff in the days leading up to the Capitol attack.

The committee said it would resume public hearings in July, with at least two more sessions scheduled. Those hearings are expected to detail how extremist groups like the Proud Boys planned the attack on Congress and how Trump failed to act to stop the violence once it erupted on 6 January.

“These efforts were not some minor or ad hoc enterprise concocted overnight,” said congresswoman Liz Cheney, the panel’s Republican vice-chair. “Each required planning and coordination. All of them were overseen by President Trump.”