The House select committee investigating January 6 appears to believe the Capitol attack included a coordinated assault perpetrated by the Oath Keepers and the Proud Boys militia groups that sought to physically stop the certification of Joe Biden’s election victory.

The panel’s working theory – which has not been previously reported though the justice department has indicted some militia group leaders – crystallized this week after obtaining evidence of the coordination in testimony and non-public video, according to two sources familiar with the matter.

Counsel on the select committee’s “gold team” examining Donald Trump, the “red team” examining January 6 rally organizers, and the “purple team” examining the militia groups, are now expected to use the findings to inform the direction for the remainder of the investigation, the sources said.

The panel has amassed deep evidence about the connections between the connections between the Oath Keepers and the Proud Boys in recent weeks after it obtained hours of non-public footage of the leaders of the militia groups in Washington ahead of the Capitol attack, the sources said.

And the select committee has also now heard testimony from award-winning documentary film-maker Nick Quested on Wednesday about contacts between the militia group leaders, far-right political operatives and the Save America rally organizers, the sources said.

The information, which could play a large role in establishing for the select committee whether Trump oversaw a criminal conspiracy as part of his efforts to overturn the 2020 election, is being viewed internally as a significant breakthrough, the sources added.

Most crucially for the panel, it could form part of the evidence to connect the militia groups that stormed the Capitol on 6 January to the organizers of the Save America rally that immediately preceded the attack – who in turn are slowly being linked to the Trump White House.

In essence, the sources said, the select committee now appears to have the same degree of evidence as secured by the FBI and the justice department referred to in recent prosecutions for seditious conspiracy and other charges related to the Capitol attack.

A spokesperson for the panel declined to comment on witness testimony.

The gold, red and purple teams have been focused on the video footage for several weeks, the sources said, with initial attention turned towards a now-infamous meeting between the militia group leaders in a parking garage near the Capitol on 5 January.

But the select committee was unable to discern from the video whether the militia group leaders even discussed the Capitol or their plans for January 6 at that rendezvous, the sources said, and suspect the meeting was a set up to provide them an alibi.

The panel has reviewed the tape repeatedly, the sources said, and House investigators have come away with an uneasy feeling that Henry “Enrique” Tarrio, the former leader of the Proud Boys, sought to have the meeting documented to later absolve himself of wrongdoing.

Tarrio last week pleaded not guilty in a separate DoJ prosecution that accuses him of organizing the Capitol attack. The indictment states Tarrio on 4 January told other Proud Boy members: “I didn’t hear this voice note until now, you want to storm the Capitol.”

The select committee has instead become more interested recently in communications both between the militia group leaders and the purported January 6 rally organizers, including Ali Alexander and far-right media personality Alex Jones, the sources said.

That topic was one of the central lines of inquiry that the gold, red and purple teams attempted to establish during a seven-hour recorded interview with Quested, the source said.

At that interview, the select committee also examined in excruciating minute-by-minute detail a 17-minute edited clip of footage shot by Quested that documented the Capitol attack, and video that tracked Alexander’s movements around the Capitol building, they said.