The leader of the Proud Boys extremist group was sentenced to more than five months in jail for burning a Black Lives Matter banner that had been torn down from a historic Black church and for bringing two high-capacity firearm magazines into the nation’s capital days before the 6 January Capitol attack.

Although government prosecutors had requested that Enrique Tarrio receive a sentence of three months in jail after pleading guilty, a District of Columbia judge on Monday said that punishment was insufficient.

“Mr Tarrio has intentionally and proudly crossed the line from peaceful protest and assembly to dangerous and potentially violent criminal conduct,” Judge Harold Cushenberry said at the sentencing hearing, adding that Tarrio had “betrayed” democratic values.

The judge said that Tarrio’s expressions of remorse and his claims that he had not fully realized what he was doing were “not credible” and in some cases contradicted by video evidence.

Tarrio was arrested on 4 January while on his way to Washington DC, two days before thousands of supporters of Donald Trump, including prominent members of the Proud Boys, descended on the US Capitol and disrupted the certification of the electoral college vote.

Police had pulled Tarrio over on a warrant for vandalizing a Black Lives Matter sign stolen from the Asbury United Methodist church in downtown DC the previous month.Authorities said the banner had been stolen by Proud Boys membersand set ablaze using lighter fluid. Tarrio had posted a picture of himself holding an unlit lighter on the social media platform Parler and admitted days later in an interview with the Washington Post that he joined in the burning of the banner.

When police pulled Tarrio over, officers found two unloaded magazines emblazoned with the Proud Boys logo in his bag. Tarrio said, according to a police report, that he sells the clips and the ones he was carrying were purchased by a customer. Tarrio was quickly released but ordered to stay away from Washington, and law enforcement later said he had been picked up in part to help quell potential violence.

Tarrio pleaded guilty last month to destruction of property and attempted possession of a large-capacity ammunition feeding device. A police spokesman told the Associated Press in December that investigators were probing the events as potential hate crimes, but no hate crime charges were filed.

In Monday’s hearing, the Rev Ianther Mills, the senior pastor of Asbury United Methodist church, described the “stress, anxiety, frustration, anger and terror” her congregation experienced as a result of seeing their church’s banner destroyed by a mob of violent men roaming through Washington, and then seeing how videos of its destruction were shared and celebrated on social media.

The banner-burning was reminiscent of “visions of slavery, the Ku Klux Klan, lynchings and their public spectacle, cross-burnings”, Mills told the court.

“This was deliberate and planned,” she said. “Who carries a bottle of lighter fluid to a peaceful demonstration?”

Tarrio’s lawyer, Lucas Danise, said his client was “extremely sorry” for what he had done and that the Proud Boys leader “wasn’t thinking clearly”. He asked the court to sentence Tarrio to community service in Florida in lieu of jail time.

Tarrio himself, clean-shaven and wearing glasses, told the court that he was sorry for his actions, calling them a “grave mistake”.

He addressed Mills directly, saying that he wanted to “apologize profusely” to her.

“I heard the grief in her voice,” Tarrio said. “What I did was wrong.”

Tarrio’s remarks in court were markedly different from the recent posts on his Telegram channel, which claimed the weekend before his sentencing that he was planning to appear at a far-right rally in Portland on Sunday that turned violent, and included a photograph of riot gear, including a gas mask and a tactical vest with the Proud Boys logo, with the caption, “Let’s rock!”

Cushenberry, a Reagan appointee, said that Tarrio’s claims that he had not realized what he was doing were not believable, and that his previous criminal history should also be taken into account.

Tarrio “could not have cared less about the laws of the District of Columbia”, Cushenberry said during the sentencing. “He cared about himself and self promotion.”

The judge also criticized government prosecutors for failing to properly document the costs the church incurred to hire private security in the wake of its targeting by Tarrio and other Proud Boys, and said he could not require Tarrio to pay more than $5,000 in restitution for those security costs because of the lack of documentation from the prosecutors.

Tarrio’s sentencing comes as authorities have narrowed in on the Proud Boys and other extremist groups, such as the Oath Keepers, in their investigation into the 6 January attack on the Capitol that sent lawmakers running and injured dozens of law enforcement officers. Members of the Proud Boys face some of the most serious charges among the more than 600 people being prosecuted in connection with the insurrection.

About three dozen people charged have been identified by federal authorities as Proud Boys leaders, members or associates. In one case, four group leaders have been charged with conspiring to impede the certification of Joe Biden’s election victory. Tarrio has not been charged in the Capitol attack.

Meanwhile, Proud Boys have continued to engage in volatile, violent street demonstrations, including in Portland and Los Angeles.

It was revealed in court records recently that Tarrio had worked undercover and cooperated with investigators after he was accused of fraud in 2012. After Tarrio’s 2012 indictment for participating in a scheme involving the resale of diabetic test strips, he helped the government prosecute more than a dozen other people, the records show.