Jon Karl reveals the office ransacked most on Jan. 6 and what it exposes about the insurrection

While speaking to the Washington Post about his new book "Betrayal," ABC News reporter Jonathan Karl revealed that one of the offices most ransacked in the U.S. Capitol on Jan. 6 tells a lot about the aims of the attackers.

While it's clear that many of President Donald Trump's supporters were caught up in the moment, it was also clear that a subset of those had very specific goals to accomplish on Jan. 6.

According to Karl, the Senate Parliamentarian's office was the most pillaged among the other rooms in the Capitol. CNN's Ali Zaslav posted a video of the office at the time. Karl explained that it was clear those going through the office were looking for something specific and he thinks it was the Electoral College ballots.

The book describes the ceremony of Jan. 6, with "three dark and shiny mahogany boxes brought in by the parliamentarian's office to be carried along as the senators walked over to the House. The boxes looked like relics from a time long past—each one held shut by wide leather straps with brass clasps and locked with a skeleton key."

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It was then that back at the rally in the White House Ellipse, Trump announced that he was going to lead his supporters to the Capitol building. Sen. Roy Blunt (R-MO) was responsible for the day's events as the chairman of the Senate Rules Committee.

"I thought it was the case that the president can come on the Senate floor anytime he wants to, but the president can come on the House floor only when invited," Blunt told Karl. House Speaker Nancy Pelosi (D-CA) didn't invite Trump to the House, nor was she about to. Blunt explained that if Trump was headed to the Capitol it would only be in the Senate, and members weren't there as they were headed to the House for the joint session that counts the Electoral College ballots.

A small group was already outside of the Capitol, but a large crowd of Trump's supporters was en route to the building. Around then, the FBI and Capitol Police responded to reports of explosive devices outside of the Democratic and Republican Party headquarters.

As the chambers were being evacuated, a Parliamentarian staffer had the wherewithal to save the ballots as they raced from the chamber, Karl recalled. Wherever the members and staff were evacuated, the ballots were with them.

"I believe that those rioters who were very keenly focused--this was not a protest, it wasn't--this was an effort to stop a transition of power," said Karl. "I believe they were searching for those ballots, with the intent of destroying them, and they were saved, again, by a junior staffer who's named--didn't want her name to be used, doesn't want to be highlighted for doing this. But again, that small step, what would have happened?"

He explained that if the insurrectionists were able to steal the ballots they could always be replaced, but the Constitution is specific about votes being done by certain dates and signatures being received and authorized by certain dates. There's no legal framework to deal with what could unfold if the ballots were taken by the attackers. It would clearly go to the Supreme Court, he explained, but who would do that? What kind of lawsuit would be filed?

READ MORE: Trump sets off alarm bells with talk of being 'reinstated' to presidency

While the staffer ensured it didn't happen, after the insurrection it was discovered that a website that posts historical maps of the Capitol was being read all over the country.

A Washington, D.C. history website that posts photos, maps and other information about the Capitol saw a dramatic increase in readership in the days leading up to Jan. 6.

Elliot Carter, who runs the website WashingtonTunnels.com, was worried that people were trying to find escape routes or entry points to the building for the attack. His concern made its way to leadership in the U.S. Capitol Police.

"These people were suddenly obsessed with the Capitol building," Carter said in August.

READ MORE: Giuliani was 'manic' during debate prep — desperately trying to get people to watch Hunter Biden video

While it's possible the attackers wanted to figure out escape routes for officials, the fact that the Parliamentarian's office was the most destroyed makes Karl think this was part of the plan all along.

"Betrayal" is on sale now.

IN OTHER NEWS: Jon Karl talked with the Washington Post's about the final days of Trump's presidency

Jon Karl talked with the Washington Post's about the final days of Trump's presidencywww.youtube.com