Federal prosecutors in Charlottesville have charged four people tied to violent unrest during a far-right rally in the city last year.

The four men, connected to the white supremacist group Rise Above Movement, were all arrested in California on Tuesday morning and charged with rioting and conspiracy to riot.

At a press conference on Tuesday, US attorney Thomas Cullen named the four as: Cole White, Benjamin Daley, Michael Miselis and Thomas Gillen. Charging documents stated that all four attended a torchlight rally at the University of Virginia campus on the evening of 11 August 2017 and a march the following day. Both events turned into violent clashes between white nationalists and counterprotestors.

Prosecutors accused the four men of being “among the most violent individuals present” during the unrest, alleging they had “travelled to Charlottesville with the intent to encourage, promote, incite, participate in, and commit violent acts in furtherance of a riot”.

The Rise Above Movement was the focus of an in-depth investigation from ProPublica, a not-for-profit news organization, which identified members of the group and documented their violent activity in Charlottesville.

Daley and Gillen were among the white supremacists who chanted “You will not replace us! Jews will not replace us!” during a white supremacist tiki torch march across the University of Virginia campus on 11 August, ProPublica reported.

Footage from the tiki torch march was widely shown around the world, shocking Americans with its depictions of unabashed white supremacists marching bare-faced in public.

The 2017 ProPublica investigation found that American law enforcement officials had taken little action in response to the Rise Above Movement’s repeated public acts of violence, which the group proudly documented in online videos, even though the group’s leaders had violent criminal histories.

Federal prosecutors said the reporting played a central part in the criminal investigation, which remains ongoing. But Cullen also raised questions about how much more time federal prosecutors would be able to devote to holding white supremacists accountable for violence last August. “We have limited resources,” Cullen said, asking later: “How many of these cases can we do?”

Heather Heyer, a 32-year-old legal assistant from the city, was killed on the second day of violence after a white supremacist, James Fields Jr, drove his car into into a crowd of counterprotesters. Fields has pleaded not guilty to second-degree murder. The charges unveiled on Tuesday did not relate directly to Heyer’s death.

The investigation into the four men took more than a year because federal officials had to process an enormous amount of video footage of the violent clashes, Cullen said. This included cellphone footage, surveillance video, and film from journalists.

“There was an incredible volume and amount of digital evidence,” Cullen said, adding that prosecutors parsed more footage than the investigation into the Boston marathon bombing in 2013.

White supremacists have continued to claim that their violent attacks on Charlottesville counterprotesters and black residents were merely “self-defense”, and Cullen, a Trump appointee, said that investigators had worked slowly in part because they had to assemble evidence that the men charged had not been defending themselves in the incidents they reviewed.

“We had to convince ourselves and the court that in this particular case, there was no provocation,” Cullen said.

The violence in Charlottesville led to sustained criticism of president Donald Trump, himself endorsed by a number of high-profile white supremacists during the 2016 presidential election. In the aftermath Trump blamed both sides for instigating violence.

“You had some very bad people in that group,” Trump said of the white supremacist protesters, “but you also had people that were very fine people, on both sides”.