The House January 6 select committee is expected to hold its final public hearing next Wednesday, with the congressional investigation into the US Capitol attack nearing its conclusion as staff counsel prepare to produce an interim report of its findings before the 2022 midterm elections.

The specific topic of the final hearing that the panel’s chairman, Congressman Bennie Thompson, will convene starting at 1pm is unclear.

But the select committee is expected to make headway on some of the most pressing questions about January 6 that remain unanswered since the panel last convened in July and made the case that Donald Trump violated the law by refusing to take action to call off the Capitol attack, sources said.

The principal issues at play include whether there was a concrete through-line from the former president to political operatives like Roger Stone and Michael Flynn, who were in close contact with the far-right extremist groups – including the Proud Boys and Oath Keepers – that stormed Congress.

The select committee has found some circumstantial evidence about such ties and previously revealed that Trump directed his then White House chief of staff, Mark Meadows, to call both Stone and Flynn the night before January 6 as the extremist groups finalized their plans for the day.

Another issue for House investigators is whether Trump’s ouster of former defense secretary Mark Esper was an effort to install in his place a loyalist who might have had no objection to using the national guard to seize voting machines or delay their deployment to stop the Capitol attack.

The select committee has viewed the plot to seize voting machines – suggested by Flynn during a contentious White House meeting in December 2020, hours before Trump sent a tweet urging his supporters to attend a “wild protest” on January 6 – as a crucial moment in the overall timeline.

House investigators have also spent time in recent weeks examining Microsoft Teams chats and emails sent between Secret Service agents on security details for Trump and former vice-president Mike Pence that day, as well as discussions about invoking martial law even after the Capitol attack.

The hearing on Wednesday is likely to touch on some of those issues, the sources said, in the last opportunity for the select committee to show potential culpability by Trump and Republican members of Congress on national television before the midterm elections take place in early November.

With their control of the House and Senate hanging in the balance, this hearing is also widely being seen on Capitol Hill as the final chance for Democrats to persuade voters that the midterms are a referendum on the Republican party’s role in January 6.

Part of the reason the Wednesday hearing is expected to be the final one is because next week is the last that the House is in session until the midterms, and the panel was reluctant to schedule an event during campaign season, when committee members like Elaine Luria face uphill re-election battles.

The select committee is also starting to shift its focus away from the made-for-television hearings – which have required time-consuming preparation and rehearsals – and towards putting together an interim report in the coming weeks as well as a final report by the end of the year.

The panel remained undecided on the final direction of each of the reports, the sources said, as well as whether to make a criminal referral to the justice department against Trump and key aides, including his former lawyer John Eastman, who orchestrated the fake elector scheme.

Once a major priority, the need for such a referral appears to have diminished in recent weeks. Subpoenas reviewed by the Guardian show the justice department is pursuing at least three investigations examining January 6 and issued more than 30 subpoenas to top Trump aides.