The man taken into custody by a federal task force appeared before a federal judge Wednesday, and prosecutors don't want him released.
Federal agents arrested Paul Miller Tuesday after swarming his residence in South Florida.
Prosecutors are accusing him of possessing a gun when he was a felon in 2018, and for this he faces a federal weapons charge.
On Wednesday afternoon, Miller was in the back of the Broward County Jail, where he'd been held overnight.
He appeared on a Zoom call with the federal magistrate, prospectors, and a federal public defender.
"I am very sorry about this," Miller told the judge. "I really am."
Cell phone video taken by a neighbor showed a large number of federal agents and Fort Lauderdale Police in front of Miller's house as they took him into custody.
"The whole street was blocked with vehicles," one neighbor, Angeline Robinson, told NBC 6. "They were undercover cars, the police."
The Anti-Defamation League's Center on Extremism has identified Miller as a "volatile white-supremacist-accelerationist. COE tracked him to Fort Lauderdale and shared significant intelligence with federal law enforcement before today's arrest."
NBC News reported that images of Miller had appeared on social media in posts that appeared to show his support of right wing extremist groups, including the Proud Boys.
The alleged weapons violation Miller is facing normally allows the person charged to post bond and leave jail, but that will not be the case here.
The federal prosecutor Wednesday indicated that the U.S. Attorney wanted Miller held until he goes to trial.
The director of the FBI told Congress Tuesday that stopping white supremacist groups is a top priority, and agents are still investigating involvement in the Capitol riots.
Miller will be held until Friday, when another hearing is scheduled. Federal agents and prosecutors are expected to reveal more information about why Miller is a flight risk then.
For now, Miller will be presumed innocent. He is in the process of hiring a lawyer, and has reportedly reached out to Mark O'Mara, the attorney who worked for George Zimmerman.
NBC 6 contacted Mr. O'Mara and did not receive a response about whether he will represent Miller.