Sullivan, who is the founder of Insurgence USA, a social justice group that calls itself anti-fascist and protests police brutality, was detained by Washington police for about an hour and a half Thursday night, a day after he talked to local and national media about what he witnessed Wednesday.
Sullivan said he also intended to "support the Black community" with his attendance, but also feels it's "important to understand" those who were protesting in support of President Donald Trump. He said he was on the "front lines" of the protest as it turned from a peaceful march into a violent storming of the Capitol.
That was not an impromptu act, Sullivan said.
"As far as them storming the Capitol, I knew that was going to happen," he said. "I'm on chats that are underground that are sending out flyers that are just like, 'Storm all Capitols on the 6th.' It wasn't anything that was secret. It was something that was out there ... and they did it."
Sullivan said he also made his way inside the Capitol during the riot and witnessed the shooting death of protester Ashli Babbitt, and the Twitter account for Insurgence USA retweeted video from someone with Sullivan that shows the shooting and the aftermath.
"I have video of it," he said, describing in detail seeing the flash of the gun, the bullet strike Babbitt, and Babbitt's reaction as she died there on the floor. "I am hesitant to post it. ... It's something I have to take in. I hope that people get a grasp of that situation. Whoever shot her, maybe should be held accountable. I guess that's up to the law to decide."
When he was asked if he was a member of Antifa, as he has used the hashtag in his social media posts, he said he understands where there could be confusion.
"If people are saying I'm Antifa, as far as a terrorist organization, I'm not," he said. "Am I anti-fascist? We all are anti-fascist. And that's what we should all strive for being. I have my own organization, Insurgence USA, and that's what it is for. That's really what it is."
Sullivan, 26, faces two criminal charges stemming from a protest he organized in Provo last June.
Charging documents say Sullivan recorded several hours of the protest and is seen in the recordings "kicking vehicles and threatening drivers" and directing protesters to block intersections.
During that protest, a Provo man, 60, was shot in the elbow after protesters blocked his vehicle. Sullivan later admitted to police that he knew who the gunman was but failed to report it to authorities, according to the charges.