Stewart Rhodes, founder of the far-right militia group Oath Keepers, has been sentenced to 18 years in prison over his role in the January 6, 2021 US Capitol riot.
While prosecutors had demanded for 25 years, this is the longest prison sentence yet given to a Capitol rioter.
Along with Rhodes, who was convicted on charges of seditious conspiracy and other crimes, a second Oath Keepers member, Kelly Meggs was also sentenced to 12 years in prison.
Thursday's sentences are the first handed down in over a decade for seditious conspiracy in the US.
"What we absolutely cannot have is a group of citizens who -- because they did not like the outcome of an election, who did not believe the law was followed as it should be -- foment revolution," CNN quoted District Judge Amit Mehta as saying before handing down the sentence.
"That is what you did. I dare say, Mr. Rhodes -- and I never have said this to anyone I have sentenced -- you pose an ongoing threat and peril to our democracy and the fabric of this country.
"I dare say we all now hold our collective breaths when an election is approaching. Will we have another January 6 again? That remains to be seen," he added
Judge Mehta said Rhodes, the 58-year-old former US Army paratrooper and Yale-educated lawyer, expressed no remorse and continues to be a threat.
"A seditious conspiracy, when you take those two concepts and put it together, is among the most serious crimes an American can commit. It is an offence against the government to use force. It is an offence against the people of our country."
Earlier on Thursday, Mehta ruled that Rhodes' actions amounted to domestic terrorism.
"He was the one giving the orders. He was the one organising the teams that day. He was the reason they were in fact in Washington D.C. Oath Keepers wouldn't have been there but for Stewart Rhodes, I don't think anyone contends otherwise. He was the one who gave the order to go, and they went."
At the hearing, Rhodes claimed he was a "political prisoner" and insisted that the Oath Keepers were standing in opposition to people "who are destroying our country", the BBC reported.
Rhodes founded the Oath Keepers in 2009. He began a campaign to reject the results of the election two days after the November 2020 vote, while ballots were still being counted.
Armed members of the anti-government group showed up at a number of protests and standoffs, and eventually became staunch supporters of former US President Donald Trump.
Dozens were present at the riot.
In January this year, four other Oath Keepers were convicted of seditious conspiracy and four members of the far-right Proud Boys were convicted on the charge earlier this month.
In total, more than 1,000 people have been arrested in connection with the riot, and more than half have pleaded guilty to crimes including assault, theft, weapons charges, trespassing and obstructing an official proceeding.
Around 80 have been found guilty following a trial, according to the US Justice Department.
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