WASHINGTON — On the afternoon of Jan. 6, 2021, shortly after President Donald J. Trump took to Twitter to tell the mob of his supporters assaulting the Capitol that “you have to go home now,” someone used a White House landline to call the phone of one of the rioters, according to a new book from a former staff member of the House Jan. 6 committee.
The book, written by Denver Riggleman, who was also previously a Republican member of the House from Virginia, did not name the man whose phone was called by the White House. But in an interview on Monday, Mr. Riggleman said he and his staff determined that the phone belonged to Anton Lunyk, 26, of Brooklyn, who was later charged with breaching the Capitol and sentenced to a year of probation.
The call lasted nine seconds and took place at 4:34 p.m.
Mr. Lunyk’s name was reported earlier by CNN. A lawyer for Mr. Lunyk did not respond to requests for comment.
In an appearance on Sunday night on “60 Minutes” on CBS, Mr. Riggleman referred to the incident as an “aha moment” — but in the interview Monday he said he was not willing to call it a “smoking gun” showing a connection between rioters and the Trump White House.
He said he understood that Mr. Lunyk had denied knowing about a call from the White House that afternoon.
“Anton Lunyk has said he doesn’t know about the call and things of that nature. That’s fine,” Mr. Riggleman said. “The data validates that the call happened.”
Mr. Riggleman described the previously unreported call in his new book, “The Breach,” in which he repeatedly highlights connections between the Trump White House and those involved with the attempts to overturn the 2020 election.
Mr. Riggleman pointed to communications the committee obtained showing Mark Meadows, the White House chief of staff, exchanging text messages with Phil Waldron, a retired Army colonel with a background in information warfare who had circulated a plan to overturn the 2020 election.
He also focused extensively on Roger J. Stone Jr., the political operative and ally of Mr. Trump’s. He called Mr. Stone “one of over 20 high-priority targets who fought our requests for call detail records in court.”
The book’s release has frustrated and angered some committee members — and sparked a public dispute.
In his book, Mr. Riggleman described his frustration with members of the committee not being aggressive enough.
He argued that the panel would not invest the millions of dollars necessary to deeply explore connections between Trump’s inner circle and people associated with violent domestic extremist groups such as the Oath Keepers and the Proud Boys.
He said he was cut out of meetings of top staff members, and demanded to be given access. He questioned why some Democrats — including Representatives Zoe Lofgren and Adam B. Schiff of California and Jamie Raskin of Maryland — were seated on the committee.
And he said Representative Liz Cheney, Republican of Wyoming and the committee’s vice chairwoman, tried to get him to back off investigating Justice Clarence Thomas and his wife, Virginia Thomas. But he acknowledged that the primary evidence he cited for his suspicions about Justice Thomas, communications linked to a “cthomas” email address, turned out not to be from him but from a Republican operative.
Tim Mulvey, a spokesman for the committee, said the panel’s investigators were aware of Mr. Riggleman’s statements, both on “60 Minutes” and in his book.
“They haven’t gone ignored,” Mr. Mulvey said. “The committee has aggressively pursued those leads and gathered additional facts, some of which have proved relevant and some of which have not. The committee’s investigation continues.”
Mr. Mulvey also said Mr. Riggleman “had limited knowledge of the committee’s investigation. He departed from the staff in April prior to our hearings and much of our most important investigative work.”
The committee is expected to interview Ms. Thomas in the coming weeks.
Mr. Riggleman said his goal is not to fight with his former colleagues but to highlight areas that need more investigation.
“The committee is doing heroic work,” Mr. Riggleman said. “I was concerned at first about the committee, talking about early in 2022. But after seeing the hearings, and knowing what we contributed to that, they’ve been incredibly impressive.”
Mr. Riggleman also said he did not have regrets about using committee materials to publish a book.
“The data belongs to the American people,” he said.