Last month, Representative Marjorie Taylor Greene, Republican of Georgia, mentioned Mr. Epps — and his supposed role in fomenting the Capitol riot — during a hearing in Atlanta held to determine whether she should be labeled an “insurrectionist” and barred from office under the Constitution.

The recordings of Mr. Epps and Mr. Samsel were released by the government last week as a discovery disclosure to scores of defense lawyers representing people charged with crimes in connection with the Capitol attack. A spokesman for the Justice Department did not respond to a request to explain why prosecutors have held on to the material so long and decided not to make it public.

Right-wing chatter about Mr. Epps, who is 60 and runs a wedding and event venue in Queen Creek, Ariz., began last spring after videos of him at a pro-Trump rally in Washington started to circulate online. Aside from the clip with Mr. Samsel, Mr. Epps was caught on video standing in a crowd of Trump supporters on the night of Jan. 5, 2021, urging his compatriots to “go into the Capitol” the next day.

At a hearing in October, Representative Thomas Massie, Republican of Kentucky, showed the clip of Mr. Epps encouraging the crowd and used it to question Attorney General Merrick B. Garland about whether federal agents had acted as agitators on Jan. 6.

The story about Mr. Epps gained further traction near the one-year anniversary of the Capitol attack when the Fox News anchor Tucker Carlson featured it in a documentary called “Patriot Purge,” which suggested that the Capitol attack might have been a “false flag” operation by the government.

Not long after, questions about Mr. Epps were raised again at a Senate hearing — this time by Senator Ted Cruz, Republican of Texas.

“There are a lot of people who are understandably very concerned about Mr. Epps,” he said.

According to the people who have heard the recording of Mr. Epps, he told the F.B.I. during his call that instigators might have been in the crowd outside the Capitol on Jan. 6. But he explained that he was not one of them and did not suggest that anyone who might have encouraged the mob that day was working for the government.