A pro-Trump demonstrator who admitted hitting protesters at a far-right rally received help and support from California police, who worked with him to prosecute leftwing activists, records show.

Documents and testimony in a trial surrounding a rightwing demonstration in Berkeley reveal that police and prosecutors pursued charges on behalf of Daniel Quillinan, a conservative activist who has posted fascist memes and came to the event with Kyle Chapman, now a celebrated figure amongst the “alt-right”. The authorities consistently treated Quillinan as a victim even though he was visibly armed with a knife, a wooden “shield” and a “flagpole” – and had told law enforcement that he “hit someone in the head”, according to court files.

Daniel Quillinan. Photograph: Handout

The resulting criminal trial against five anti-fascist protesters – who are accused of assaulting Quillinan during a roughly 15-second altercation – is, according to activists, the latest example of US law enforcement aggressively targeting leftwing demonstrators and favoring members of the far-right after violent clashes. In another California case, police have worked directly with neo-Nazis to go after counter-protesters, including a black activist stabbed at a white supremacist rally.

“This makes a pretty clear statement of choosing sides,” Dustin Sawtelle, one of the anti-fascist defendants, said in an interview this week before the trial began. “We figured maybe they were trying to use charges as a scare tactic ... It feels like they have to prosecute somebody.”

At the trial in a crowded Oakland courtroom, defense attorneys argued that local police were tolerant of the pro-Trump violence on 4 March last year, that Quillinan was an armed aggressor and fascist provocateur, and that prosecutors lacked basic evidence about the alleged assault. The prosecutor, along with several police witnesses, argued that the men were observed attacking Quillinan with punches and kicks during a short confrontation outside of the rally.

The event, billed as a “March for Trump” and “free speech” event, attracted interest from members of the alt-right and was linked to the Proud Boys, a far-right pro-Trump group of self-proclaimed “western chauvinists” that has been classified by watchdogs as a hate organization. Quillinan arrived at the rally wearing a red Trump hat, and a shirt referencing the Chilean dictator General Pinochet and a far-right meme with the words “physical removal”, which he said in court referred to the removal of “communists and Democrats”.

Facebook Twitter Pinterest Dustin Sawtelle, one of the defendants. Photograph: Sam Levin/The Guardian

Quillinan testified that he was “conservative” and pro-Trump, but said he was not “alt-right” nor a white nationalist and alleged that his shirt and online posts referencing fascism were “jokes”. The audience of anti-fascists supporting the defendants, who some have called the “Berkeley 5”, groaned loudly when the prosecutor described the rally as a “free speech” event.

Police video showed that when Quillinan arrived, an officer noted he had a knife, but said he could “keep it”, despite a local ordinance restricting the carrying of “dangerous weapons”, said the defense attorney, Shanta Driver.

Quillinan said in court that he brought the knife as a “deterrent” and the wooden board he carried like a shield was a “poster”. On cross examination, he admitted he might have hit someone with the board “by accident” and also said he had used his pole to try to break up fights and struck two people.

Law enforcement is aware of Quillinan’s use of the pole as a weapon. Prosecutor James Logan wrote that Quillinan admitted “he swung his flagpole” and at one point struck a man in the head. Quillinan said he offered to give the man money after he realized he was conservative.

When the alleged attack by the five defendants occurred, Quillinan was receiving medical aid for a head injury. Quillinan and Jesse Grant, a police officer who was nearby, testified that the anti-fascists were walking by when one kicked Quillinan and then others started punching and kicking. The defense, however, said Quillinan tripped one of the men and then hit him with his shield. Both sides said the interaction was brief.

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Sergeant Grant testified that he couldn’t specify the exact actions of several of the defendants, saying it was a “scrum” and “arms and legs were flying”. A fire captain present during the incident testified that he couldn’t recognize or identify the defendants seated in the courtroom.

Quillinan had also originally said one of his attackers had “red hair”, which does not match any of the defendants. Asked about this discrepancy in court, he said: “I may have misremembered.”

In an interview with Quillinan the day of the incident, Grant raised the idea of charges, according to a recording, saying: “The people who attacked you – do you want them to go to jail?”

“Very much so,” Quillinan replied.

Facebook Twitter Pinterest The group including Jeff Armstrong (pictured) has been dubbed the Berkeley 5. Photograph: Sam Levin/The Guardian

Jeff Armstrong, another defendant, told the Guardian that he showed up to the march to help protect people from rightwing violence: “We went to do medical aid for people and also to defend people who can’t defend themselves.”

Police and prosecutors declined to comment. Quillinan, who was ordered not to speak about the case while the trial is ongoing, could not be reached.

It’s unclear if any rightwing demonstrators faced assault charges for the 4 March fight. Chapman, the rightwing activist, was charged with possession of a leaded stick in a case that is still pending.

Even if the five anti-fascist protesters are acquitted, the case that has dragged on for more than a year has already impacted their lives, said Sawtelle, a 41-year-old tattoo artist and martial arts teacher. He said his personal information was posted online, leading to threats, and that he lost a job as a result of the charges. He said he has also been forced to be more cautious about his activism and participation in protests.

“I think that’s part of the tactic – to get people away from these things,” he said, adding: “I don’t plan on quieting down.”