The House select committee investigating the Capitol attack on Wednesday subpoenaed Donald Trump’s former White House senior adviser Peter Navarro, escalating its inquiry into the former president’s efforts to return himself to office and the January 6 insurrection.

The move to pursue Navarro, who helped finalize the scheme to stop the certification of Joe Biden’s election win with political operatives at the Willard hotel in Washington DC, suggests the panel is edging ever closer to examining potential culpability for Trump.

Congressman Bennie Thompson, the chairman of the select committee, said in the subpoena letter to Navarro that House investigators wanted to depose him since he could potentially speak to what Trump knew in advance of plans to stop the certification on January 6.

“Navarro appears to have information directly relevant to the select committee’s investigation,” Thompson said. “He hasn’t been shy about his role in efforts to overturn the results of the 2020 election and has even discussed the former president’s support for those plans.”

Thompson suggested in the letter that Navarro should be free to speak to the panel without concerns about executive privilege or other legal impediments, since he discussed the events of 6 January in his book In Trump Time, on his podcast and with reporters.

The former White House adviser is of special interest to the panel, according to a source close to the investigation, as Navarro had the ear of the former president and, simultaneously, was in regular contact with the Willard operatives that formulated the plot.

Navarro had been briefed by the Willard operatives – led by former Trump attorney Rudy Giuliani and former Trump aide Steve Bannon – about their plan to have Mike Pence declare Trump the winner, or have the majority GOP delegation House vote for Trump in a contingent election.

The Guardian first reported that after Trump was briefed on the scheme – which Navarro named the “Green Bay Sweep” – he told the Willard operatives just hours before the Capitol attack to find ways to stop Biden’s certification from happening.

The former White House adviser also reported back to the Willard operatives on the morning of January 6 about the size of the pro-Trump crowds that would storm the Capitol later that afternoon, according to a former Trump official familiar with Navarro’s actions.

As the select committee investigates whether Trump knew in advance of plans to violently stop Biden’s certification from taking place on January 6, Navarro could shed light on how much of the information he received from the operatives made it to Trump, the source said.

The panel gave Navarro until 23 February to produce documents detailed in the subpoena, and ordered him to appear for a deposition on 2 March. It was not clear whether Navarro would cooperate; he did not immediately respond to a request for comment.