Federal investigators raided the home of former Trump justice department official Jeffrey Clark early Wednesday in connection with the department’s sprawling criminal investigation into efforts to overturn the results of the 2020 presidential election.

The search of Clark’s home in suburban Virginia and the seizure of his electronic devices suggested an escalating inquiry into his involvement in the purported election plot edging ever closer to Donald Trump, according to a source familiar with the matter and one of his associates.

But it was not immediately clear on Thursday what federal investigators were looking for, or which agencies were involved, though Clark was a key figure in Trump’s failed attempt to pressure the justice department into falsely declaring the election was corrupt.

The raid on Clark’s home came a day before the House select committee investigating the January 6 attack on the Capitol convened its fifth public hearing, which focused on Trump’s effort to have the justice department declare the 2020 election “corrupt” and endorse discredited election fraud claims.

In a statement, Russ Vought, the former head of the office of management and budget during the Trump administration and now the head of the Center for Renewing America – where Clark now also works – decried the search.

“Yesterday more than a dozen DoJ law enforcement officials searched Jeff Clark’s house in a pre-dawn raid, put him in the streets in his pajamas, and took his electronic devices,” Vought said, adding: “We stand by Jeff and so must all patriots in this country.”

The raid came as a federal grand jury in Washington continued to authorize subpoenas against people connected to a separate plot by Trump to apparently send fake slates of electors to Congress to obstruct its certification of Joe Biden’s election win.

In recent days, according to sources familiar with the matter, the chairwoman of the Arizona Republican party Kelli Ward, and her husband, Michael Ward, who both signed certificates falsely attesting to be the legitimate electors, received subpoenas.

The federal grand jury investigation into the so-called fake electors scheme appears to be targeting a number of Trump’s lawyers, including Rudy Giuliani and Boris Epshteyn, according to a copy of one of the grand jury subpoenas, which was obtained by the Guardian.

The role played by Clark in Trump’s plot to oust the leadership of the justice department was among the top focuses of the hearing, with the select committee tracing the timeline of how Clark almost became the top law enforcement official in the county.

Clark is a relatively unknown environmental lawyer who headed the justice department’s civil division, which defends the administration in court, among other things. He was introduced to the former president by Republican congressman Scott Perry, the panel said.

He became a key figure in Trump’s election reversal efforts when Trump urged Clark to get the justice department leadership to sign on to a letter – referred to as a “Georgia proof of concept” letter – that falsely said the department would probe election fraud claims.

The letter advised Georgia’s governor, Brian Kemp, to convene a special session of his state’s legislature to create a “separate slate of electors” in favor of Trump, in light of “significant concerns that may have impacted the outcome of the election”.

The letter was drafted by former Trump White House lawyer Ken Klukowski and Clark, the select committee said at the hearing.

Clark conveyed the letter to his superiors, then acting attorney general Jeffrey Rosen and his deputy, Richard Donoghue, who both refused to sign the letter. The aim of the letter was to give otherwise nonsense claims of fraud the imprimatur of justice department legitimacy.

Trump attempted on 2 January 2021 to strong-arm Rosen into signing the letter, according to notes of the meeting obtained by the panel, first suggesting he could dismiss Rosen, and then saying he would not fire Rosen as long as he sent the letter.

The following day, the former president appeared to have decided to fire Rosen anyway, according to White House call logs obtained by the panel, which, by 4.19pm, had started referring to Clark as “Acting Attorney General Jeffrey Clark” instead of “Mr Jeffrey Clark”.

Trump ultimately backed off from his intention to appoint Clark as acting attorney general later that afternoon on 3 January 2021, when Rosen warned him that he, Donoghue and the entire justice department leadership would resign.