▶ Watch Video: Denver Riggleman on new book, Jan. 6 committee investigation

Former Republican Congressman Denver Riggleman’s new book, “The Breach,” gives an inside account of his time working as a senior adviser for the House Select Committee investigating the Jan. 6 attack on the Capitol. 

During an exclusive interview with “60 Minutes” correspondent Bill Whitaker on Sunday, Riggleman said that someone in the White House was calling one of the rioters while the insurrection was going on. 

On Monday, Riggleman gave more details to “CBS Mornings” about that call and about why it is not known who exactly made the call. 

“It wasn’t a very long call. That’s one of the things, it was less than 10 seconds. But what I want to explain to the American people, look at the switchboard as the tech, right? It’s a desk phone somebody called, a call manager, works its way through the call manager. Really it strips that regular phone number and adds just a default number,” Riggleman said.  “When I say to the switchboard, it’s a switchboard number. Really the call is from a desk phone to somebody who’s a DOJ charged defendant.”

Specific White House phone numbers are kept secret to protect every administration. He added that it is “not probable” that former President Donald Trump could have made that call, but it’s not really known because it came from a switchboard number. 

“I would say it’s probably not probable, you know, but on the other hand we don’t know what those extensions or those numbers are,” Riggleman said. 

Riggleman’s work with the House Select Committee included analyzing 20 million lines of data, including e-mails, social media posts and phone records. 

Riggleman left the committee last April after he told “60 Minutes” it was because they wouldn’t subpoena Ginni Thomas.   

He said his work on the House Select Committee and his upcoming book have led to him getting death threats. He has also received criticism from the House Select Committee who said his work was only a smart part of the overall effort. 

Riggleman said he hopes that when people look at his book, they will consider the data that is being presented despite their own opinions. 

“I think when you look at the book, it’s data. I’m not sure why they’re doing that. I think they need to read the book and understand this isn’t a critique of the committee. There’s fear there. There shouldn’t be. What this does is support the incredible work of the committee,” he said.