A Republican member of the congressional committee investigating the January 6 attack on the Capitol said on Sunday that he believes Donald Trump’s actions surrounding the deadly riots amount to “seditious conspiracy” and “criminal involvement by a president”.

Illinois congressman Adam Kinzinger’s remarks on ABC’s This Week came after three hearings held by the House January 6 committee presented searing testimony and mounting evidence about Trump’s central role in a complex plot to overturn his defeat at the hands of Joe Biden in the 2020 presidential election.

While he was only one of at least four committee members scheduled to appear on the national news network’s Sunday talkshows, Kinzinger’s comments stood out for their candor and because they came from within the ex-president’s own political party.

“I certainly think the president is guilty of knowing what he did, seditious conspiracy, being involved in … pressuring the [justice department], vice-president [Mike Pence], et cetera,” Kinzinger said. “Obviously, you know, we’re not a criminal charges committee, so I want to be careful in specifically using that language, but I think what we’re presenting before the American people certainly would rise to a level of criminal involvement by a president.”

Kinzinger also said that Trump’s actions, as portrayed by the committee, show he “definitely” failed to maintain his oath to uphold the US constitution.

“The oath has to matter here,” Kinzinger said. “Your personal demand to stand for the constitution has to matter.”

Just three days earlier, the third of six scheduled hearings by the committee examining the Capitol attack saw a former attorney to Pence recount how Trump unsuccessfully helped pressure Pence into unlawfully blocking the congressional certification of Biden’s win on the day of the riots.

One of the prongs of that plan involved sending fake pro-Trump electors from states that Biden to substitute electors pledged to Biden, which the justice department has been investigating for months now. Another prong, broadly, centered on Trump’s relentless but baseless claims that electoral fraudsters had stolen the race from him, even as his attorney general, William Barr, dismissed that argument as complete “bullshit”.

Kinzinger said the only logical outcome to claims of a rigged presidential election was the mob of hundreds storming the Capitol – shortly after Trump urged his supports to “fight like hell” – in the attack to which a bipartisan Senate report connected seven deaths.

The congressman added that there is more where that came from unless the country can “get a grip on telling people the truth” about things like valid election results, even when their preferred candidate lost.

“There is violence in the future – I’m going to tell you,” said Kinzinger, one of two Republicans on the nine-member select committee.

As Kinzinger told This Week’s host George Stephanopoulos, the January 6 committee can’t file criminal charges against Trump. And the panel chairman, Mississippi congressman Bennie Thompson, said he doesn’t expect he and his colleagues to make a referral for charges to the justice department, which is the sole entity with the power to prosecute Trump.

Nonetheless, Kinzinger’s comments on Sunday made clear what he and others on the committee think federal prosecutors should do even without a formal recommendation for charges.

Pence himself, as of Sunday, hadn’t appeared at the January 6 hearings. But one of the Democrats on the select committee, Adam Schiff, said the panel hadn’t ruled out subpoenaing him to testify.

Trump, for his part, has condemned the work of the January 6 committee as a “one-sided witch-hunt”.

At a speech in Tennessee on Friday, he singled out Kinzinger for crying during another hearing last year about the Capitol attack.

“This guy’s got a mental disorder,” Trump said of Kinzinger. “He cries. Every time this guy gets up to speak, he starts crying.”

Kinzinger’s decision to go on the offensive against Trump – whom many Republicans still support vehemently – are not without peril. On Sunday, he recounted how someone had recently mailed to the congressman’s home a note threatening to execute him, his wife and their five-month-old son.

“This should be a position where you can tell the hard truth, and unfortunately, my party has utterly failed the American people at truth,” Kinzinger said. “It makes me sad. But it’s a fact.”