The Justice Department is examining ties among the far-right Proud Boys, Roger Stone and others over their roles in 2018 “Stop the Steal” demonstrations.
The committee also said it had evidence that some House Republicans sought pardons from President Donald J. Trump in connection with the effort to overturn the election.
Testimony disclosed by the House committee investigating the riot showed that Mark Meadows and Freedom Caucus members discussed directing marchers to the Capitol as Congress certified the election results.
The effort by the Trump ally to get an immunity deal is the latest sign of progress in the investigation, which recently brought on a well-regarded prosecutor.
Ali Alexander, who was a key figure in the “Stop the Steal” movement, said he had received a grand jury subpoena and would assist the expanding investigation.