The claims, made in congressional hearing rooms, on Fox News and at Mr. Trump’s political rallies, have largely been based on a video taken just before violence erupted at the Capitol, showing Mr. Epps at the barricades outside the building whispering into the ear of a man named Ryan Samsel.

Within moments of the brief exchange, Mr. Samsel, a Pennsylvania barber, can be seen moving forward and confronting the police in what amounted to the tipping point of the riot. Despite lacking proof for their claims, many Republicans have surmised that Mr. Epps instructed Mr. Samsel to antagonize the officers. They have also pushed the notion that because Mr. Epps has not been arrested, he must have been working for the government…

Just two days after the attack, when Mr. Epps saw himself on a list of suspects from Jan. 6, he called an F.B.I. tip line and told investigators that he had tried to calm Mr. Samsel down when they spoke, according to three people who have heard a recording of the call. Mr. Epps went on to say that he explained to Mr. Samsel that the police outside the building were merely doing their jobs, the people said.

Then in late January of last year, in an interview with the F.B.I., Mr. Samsel said much the same thing, telling investigators that a man he did not know came up to him at the barricades and suggested he relax, according to a recording of the interview obtained by The New York Times.