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Security officials testified Tuesday that they believe the Capitol riot on Jan. 6 was a "coordinated attack" as they were pressed by senators over the circumstances leading to the security failure.

Former U.S. Capitol Police Chief Steven Sund, former Senate Sergeant-at-Arms Michael Stenger and former House Sergeant-at-Arms Paul Irving, as well as Metropolitan Police Department acting chief Robert Contee, appeared before the Senate Homeland Security and Governmental Affairs Committee on Tuesday, in the first Senate hearing to examine the "security failures" that led to the breach of the U.S. Capitol last month.

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Committee Chairman Gary Peters, D-Mich., questioned the officials over whether they believed there was coordination with regard to the attack.

"These people came specifically with equipment. You’re bringing climbing gear to a demonstration, explosives, chemical spray – you’re coming prepared," Sund testified. "The fact that the group attacked our West Front 20 minutes before the event at the Ellipse ended – they were planning on our agency not being at full strength at that time."

Former U.S. Capitol Police Chief Steven Sund testifies before a Senate Homeland Security and Governmental Affairs & Senate Rules and Administration joint hearing on Capitol Hill, Washington, Tuesday, Feb. 23, 2021, to examine the January 6th attack on the Capitol. (Erin Scott/The New York Times via AP, Pool)

Former U.S. Capitol Police Chief Steven Sund testifies before a Senate Homeland Security and Governmental Affairs & Senate Rules and Administration joint hearing on Capitol Hill, Washington, Tuesday, Feb. 23, 2021, to examine the January 6th attack on the Capitol. (Erin Scott/The New York Times via AP, Pool)

Sund was pointing to former President Trump’s rally, which took place at the Ellipse near the White House just before the riots began.

Sund added that U.S. Capitol Police were "dealing with two pipe bombs, specifically set right off the edge of our perimeter to draw resources away."

"I think there was a significant coordination with this attack," Sund said.

Contee also said rioters used "hand signals and radio communication," as well as a "coordinated use" of chemicals.

"I certainly believe it was coordinated," Contee said, pointing to the "placement of pipe bombs in the area, all of those things, and plus, adding to what we know in hindsight, now, as a result of the ongoing investigation of the FBI."

"As they continue to scrub social media, we are learning more and more and more that this is clearly a coordinated effort," Contee said.

And Irving agreed.

"Based on the information provided by Contee and Sund, I would agree," Irving said. "The evidence would indicate a coordinated attack."

Peters said that extremist groups, like the Oath Keepers and Proud Boys, have been identified in intelligence reports, and that the committee plans to hold future hearings to discuss that intelligence.

The Capitol Riot followed Trump’s rally, in which he encouraged his supporters to protest Biden's Electoral College certification. 

Trump told his followers during that speech to protest "peacefully and patriotically," but critics have said that one off-hand comment does not outweigh the balance of his rhetoric in the lengthy Jan. 6 speech or in the preceding weeks, in which he said the rally would be "wild."

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Rioters had been around the Capitol for most of the day on Jan. 6, but they finally breached the building as their numbers grew about an hour after Trump's speech concluded. 

Trump was acquitted by the Senate earlier this month after a weeklong trial, following the House of Representatives on Jan. 13 voting to impeach him on one article – inciting insurrection – in connection with the Capitol riot on Jan. 6.

Trump was the first president in U.S. history to be impeached twice and the first president out of office to go through an impeachment proceeding.

Trump was acquitted, with 57 senators voting for his conviction – short of the required two-thirds majority – and 43 voting against. 

Fox News’ Tyler Olson contributed to this report.