Former President Donald Trump's aides were reportedly blindsided when the House select committee investigating the Capitol riot revealed it had subpoenaed a documentary filmmaker who had extensive access to Mr Trump and his inner circle ahead of the January 6 insurrection.

       British documentary filmmaker Alex Holden had been documenting Mr Trump and his family in the months leading up to the Capitol riot. Mr Holden revealed on Tuesday that his footage was requested by the House January 6 committee.

       According to Politico, which first reported the story, the subpoena asks for his raw footage taken on 6 January, any raw footage from interviews he conducted between September 2020 and the present day with Mr Trump, former Vice President Mike Pence, Donald Trump Jr, Ivanka Trump, Eric Trump, and Jared Kushner.

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       It also asks for raw footage "pertaining to discussions of election fraud or election integrity surrounding the 2020 presidential election”.

       The subpoena reportedly caught Mr Trump's former aides off-guard.

       "What the f*** is this?" a former top Trump 2020 official reportedly told Rolling Stone on Tuesday.

       According to Maggie Haberman of the New York Times, a "very small group of people had knowledge of this documentary project, and a lot of Trump advisers were surprised to see it existed this morning ... senior campaign officials were unaware of the project, according to one former official."

       Rolling Stone also reported that other senior officials were just learning of the documentary Tuesday morning as a result of the Politico story.

       Mr Holder said he intended to cooperate fully with the select committee.

       “When we began this project in September 2020, we could have never predicted that our work would one day be subpoenaed by Congress,” he said. "As a British filmmaker, I had no agenda coming into this. We simply wanted to better understand who the Trumps were and what motivated them to hold onto power so desperately. We have dutifully handed over all the materials the Committee has asked for and we are fully cooperating."

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       According to Mr Holden, the documentary — titled Unprecedented — was bought last year by a major streaming service and will reportedly be released as a 3-part series this summer. He noted in his statement that he was not paid by Mr Trump, his family, or his staff and that he maintained total editorial control over the project.

       The hearing continued today, with the House Select Committee advancing evidence that Mr Trump and his top officials attempted to use an "alternate electors" scheme to keep him in office.