Nick Alvear started believing in Trump “because 800,000 kids in America go missing every year – held captive, tortured and killed … enslaved sexually … I’m part of the first wave bringing awareness of this.”

It is perhaps the greatest of Four Hours at the Capitol’s many strengths that it gives space to those who were most eager for battle. They call themselves insurrectionists, while others in the BBC Two documentary that details the unfolding of the 6 January assault on the meeting place of the US Congress refer to them as domestic terrorists.

Jamie Roberts’ film (he also directed The Rise of the Murdoch Dynasty) lays out the timeline of that extraordinary day in exhaustive but never exhausting detail. Phone footage shot by Eddie Block, a member of the far-right group Proud Boys, shows them beginning to gather at 10.35am. By 12.06pm they have heard enough of Trump’s Stop the Steal speech to have started marching towards Capitol Hill. Viewers are reminded of the barely veiled exhortations to action that were ringing in their ears: “You’ll never take back our country with weakness … If you don’t fight like hell you won’t have a country any more.”

The film hears from many of those on the other side of the fight, including some of the 40 or 50 officers who did their best to hold back the 1,500-strong mob as they came up the steps and broke into the building, and from members of Congress (Republican and Democrat) and others who found themselves trapped inside. The latter include Leah Han, a staffer in Nancy Pelosi’s office, who recounts how she and her colleagues relocated from the room that bore Pelosi’s name to an anonymous office down the hall and hid under the desks as the noise of invasion got louder, hoping that they would not be killed or raped before help arrived.

The accounts of those trapped and of the officers hopelessly outnumbered outside are as harrowing as you might expect – whether they are recollected with stoicism (“For hours we were sitting there, the president not saying a word,” says Republican representative for Illinois Adam Kinzinger. “To me that was beyond the pale”) or fury (most of the officers). Foremost among the second group is Mike Fanone, who was grabbed by the mob as he and others battled for hours to keep protesters out of the tunnel that would have let them flood the building. He was Tasered and beaten before being passed back to safety. He suffered a traumatic brain injury and a heart attack. “That I and a shit-ton of my fellow officers almost lost their lives pisses me the fuck off,” he says.

The documentary passed lightly – too lightly, maybe – over the lack of preparation by Capitol and Metropolitan Police Department officials on the day, given the known combustibility of the situation and the hesitant response from the National Guard and others to pleas for reinforcement. However, overall there was a much-needed sense of the true human impact of what happened. From the outside, ruined by Hollywood spectacle as we all have been, perhaps it didn’t look that bad. Once we were taken inside – shown the mentality and mechanics of the crowd, and given the proper scale by which to judge – it was that bad, and worse.

Most chilling of all was the lack of remorse among the rioters interviewed, coupled with their unassailed – and one must presume, at this point, unassailable – devotion to the man they believe commanded them to storm the Capitol. There was also a generous portion of denial and doublethink from people like Couy Griffin, part of the Cowboys for Trump group, who insists he was standing among thousands of “peaceful patriots” and thinks that “you’re really stretching it to say it was supporters of Trump that did it … just because they have a Trump hat or a Trump T-shirt on”.

Three protesters outside the Capitol died from medical emergencies, 140 police officers were injured, one died and – since January – there have been four deaths by suicide among those who were on duty that day. The rage still visibly emanates from Fanone. “I still haven’t made sense of it,” he says, eyes blazing. “And it certainly doesn’t help when the elected leader won’t even acknowledge it occurred.”

The underlying collective testimony furnished by Four Hours at the Capitol is that the age of Trump has not yet ended – and the true day of reckoning in the United States is still to come.