Donald Trump and a lawyer who assisted with his re-election campaign were part of a “criminal conspiracy” to overturn the 2020 election, according to a court filing from the congressional 6 January US Capitol riot investigation.

       The documents, filed on Wednesday, come as the House special committee seeks to gain access to emails from John Eastman, a lawyer who helped lead Mr Trump’s “war room” challenging Joe Biden’s election win.

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       Mr Eastman reportedly proposed pressuring then vice-president Mike Pence to reject the election results, which by then had been approved by all 50 states and were awaiting an essentially symbolic certification process in Congress.

       “The facts we’ve gathered strongly suggest that Dr Eastman’s emails may show that he helped Donald Trump advance a corrupt scheme to obstruct the counting of electoral college ballots and a conspiracy to impede the transfer of power,” representatives Bennie Thompson of Mississippi and Liz Cheney of Wyoming, who chair the 6 January investigation committee, said in a statement.

       The Independent has reached out to Mr Trump and Mr Eastman for comment.

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       The filing argues that Mr Eastman can’t claim attorney-client privilege over thousands of documents he has withheld because they may have been used in the committing of multiple crimes.

       The committee says it has sound legal basis to believe that Donald Trump broke federal law by obstructing or attempting to obstruct an official government proceeding, and by interfering with government functions.

       “As the courts were overwhelmingly ruling against President Trump’s claims of election misconduct, he and his associates began to plan extra-judicial efforts to overturn the results of the election and prevent the President-elect from assuming office,” the document reads. “At the heart of these efforts was an aggressive public misinformation campaign to persuade millions of Americans that the election had in fact been stolen. The President and his associates persisted in making ‘stolen election’ claims even after the President’s own appointees at the Department of Justice and the Department of Homeland Security, along with his own campaign staff, had informed the President that his claims were wrong.”

       The step was seen as a major development by legal observers, who called the committee’s arguments a “bombshell.”

       “This is big,” former acting US Solicitor General Neal Katyal wrote on Twitter on Wednesday in reaction to the filing. “1/6 committee just said they have a good-faith belief that Trump committed crimes.”

       Mr Trump escaped sanction during his second impeachment trial, so Wednesday’s filing could mark the most significant attempt yet to punish the former president for his alleged link to the attack on the US Capitol.

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       So far, Mr Eastman, the Trump lawyer, has turned over 8,000 pages of documents voluntarily, but has withheld an even greater number.

       The 6 January committee has previously disputed that these documents are in fact protected by active attorney-client privilege, pointing to an engagement letter between Mr Eastman and the former president that was unsigned as evidence that two didn’t yet have a formal legal relationship.