Christian Secor, 22, was taken into custody in Costa Mesa on Tuesday by FBI agents, according to authorities.
The criminal complaint alleges that Secor stormed the Capitol and was seen inside the building, on the Senate floor and also sitting on former Vice President Mike Pence's chair in the Senate chambers during the insurrection.
Officials say Secor, who has openly espoused white supremacy views online, was ordered held without bail Tuesday during his first appearance in federal court in Santa Ana.
He broadcast a livestream from the Capitol, authorities said, with a username that appears to be a reference to a man who killed six people in Isla Vista, California, in 2014. Secor previously bragged that he would not be caught, officials said.
Secor is charged with five federal offenses and is among more than 200 defendants accused of participating in the siege of the U.S. Capitol, where dozens of people were hurt and one Capitol police officer later died of his injuries.
Prosecutors say pictures were taken of him on Jan. 6 wearing a Make America Great Again hat and holding an adulterated American flag. He was also seen sitting in a chair on the dais where Pence had sat and presided over the Senate as lawmakers certified Electoral College votes.
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At least 11 tipsters identified Secor to the FBI as the person seen in the images and videos, sometimes carrying a large blue "America First" flag, authorities said.
Last year at UCLA, according to court documents, Secor was repeatedly accused of inciting racism through comments and tweets about immigrants and Jews. He also founded a student group called America First Bruins at the university.
Asked for comment about the arrest, a UCLA spokesperson declined to discuss Secor specifically.
"Information on this person is not available to the public," said Bill Kisliuk, UCLA's director of media relations. "What I can tell you is that UCLA believes the Jan. 6 attack at the Capitol was an attack on our democracy. As an institution, UCLA is committed to mutual respect, making decisions based on evidence and using rational debate and not physical violence."
Meanwhile, after being acquitted last weekend, former President Trump is now facing a lawsuit in the insurrection.
The suit was filed by Mississippi Rep. Bennie Thompson and the NAACP. It accuses Trump of conspiring with far-right groups to try to prevent Congress from certifying election results.
An adviser to Trump said he did not incite any violence last month.
In nearly half of the more than 200 federal cases stemming from the attack on the Capitol, authorities have cited evidence that an insurrectionist appeared to be inspired by conspiracy theories or extremist ideologies, according to an Associated Press review of court records.
The FBI has linked at least 40 defendants to extremist groups or movements, including at least 16 members or associates of the neo-fascist Proud Boys and at least five connected to the anti-government Oath Keepers. FBI agents also explicitly tied at least 10 defendants to QAnon, a pro-Trump conspiracy theory that has grown beyond its fringe origins to penetrate mainstream Republican politics.
In at least 59 other cases, authorities link defendants to violent or extremist rhetoric, conspiracy theories or other far-right connections on social media and other forums before, during or after the Jan. 6 siege, a deeper review by the AP found.
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The Associated Press contributed to this report.