It remains unclear why Mr. Chesebro was with Mr. Jones’s group outside the Capitol or how he came to be with them. A lawyer for Mr. Jones said that Mr. Jones was unaware that Mr. Chesebro had been following his entourage that day.

Mr. Chesebro was charged this week as one of Mr. Trump’s 18 co-defendants in a sprawling racketeering indictment brought by the district attorney’s office in Fulton County, Ga. That indictment accused him of taking part in a sweeping plot to create slates of so-called fake electors pledged to Mr. Trump in several key swing states that Joseph R. Biden Jr. had won.

Mr. Chesebro also appeared as an unnamed co-conspirator in a similar federal indictment brought against Mr. Trump in Washington this month by prosecutors working for the special counsel, Jack Smith. Mr. Chesebro wrote three memos in November and December 2020, which prosecutors used to trace the evolution of the fake elector plan and an attempt to use it as part of a broader effort to pressure Vice President Mike Pence to throw the election to Mr. Trump during a joint session of Congress on Jan. 6, 2021.

Wearing a red MAGA hat, Mr. Chesebro can be seen joining Mr. Jones’s group outside the Capitol shortly before 2 p.m. that day, according to the photographs and video reviewed by The Times. The visual evidence shows he stayed with Mr. Jones, Mr. Alexander and others — including Owen Shroyer, one of Mr. Jones’s top aides — for about an hour and a half, often filming Mr. Jones on his cellphone as the group walked around the Capitol and went partly up the stairs outside the east front of the building.

Mr. Jones and Mr. Alexander were among the first “Stop the Steal” activists to draw attention from federal prosecutors investigating the Capitol riot. As early as April 2022, Mr. Jones reached out to the Justice Department in an unsuccessful effort to secure an immunity deal in exchange for information. Mr. Alexander was subpoenaed by — and ultimately testified to — a grand jury in Washington that was looking into various aspects of the attack.