The House select committee investigating the January 6 Capitol attack is expected at its first hearing on Thursday evening to connect the far-right Proud Boys and the Oath Keepers militia groups in the same seditious conspiracy, according to two sources familiar with the matter.

The move by the panel and chief investigative counsel Tim Heaphy could be one of the major revelations that comes from the hearing, which is expected to focus on the militia groups and how they made plans to storm the Capitol, the sources said.

Top members of the Proud Boys and the Oath Keepers have been charged separately by the justice department with seditious conspiracy, but the select committee’s intention to show that their efforts were connected would escalate the gravity of the plans to attack the Capitol.

The panel is understood to be able to connect the two groups in part as it got access to the Oath Keepers’ encrypted Signal messaging chats, while the first witness at the hearing, documentarian Nick Quested, who filmed the Proud Boys, overheard their planning.

Text messages released by the justice department have also shown that the two groups were in touch before January 6. Meanwhile at least one person, Joshua James, appears to have simultaneously been both a member of the Proud Boys and the Oath Keepers.

It could not be confirmed ahead of the hearing whether the select committee had the evidence to tie Donald Trump into the Proud Boys and Oath Keepers’ conspiracy. But the panel is not expected to tie Roger Stone to the conspiracy, having been unable to find any such evidence.

The role of the militia groups in the story of January 6 is important because they specifically planned to storm the Capitol to stop the certification of Joe Biden’s election win – what Trump wanted and needed after his other efforts to overturn the election failed.

The panel is expected to make its case that there was coordination between the Proud Boys and the Oath Keepers – something the panel has long believed – over the course of a hearing that will specifically zero in on the role of the Proud Boys in the Capitol attack.

A member of the Proud Boys was the first person to breach the Capitol by using a police riot shield to break through a window on the Senate side of the Capitol, and another member of the Proud Boys appeared to precipitate the first breach of police lines on January 6.

The inaugural hearing is expected to focus on Quested’s video footage of the moment that Joseph Biggs, a member of the Proud Boys indicted for seditious conspiracy on Monday, had a brief exchange with another man near the Peace Monument at the foot of Capitol Hill.

Biggs’ exchange with that man, Ryan Samsel, is widely seen as the tipping point that precipitated the riot. Samsel, who has been charged with attacking police, then walks up alone to the barricade and confronts US Capitol police officers before pushing it over.

The inaugural hearing is also expected to focus on Quested’s video of the Proud Boys charging up Capitol Hill towards the lower west plaza of the Capitol and the inaugural ceremony platform, where Proud Boys member Dominic Pezzola smashes the window with the shield.

Also during the inaugural hearing, the select committee is expected to play previously unreleased video of Trump’s top aides and family members testifying before the panel. The panel intends to show Trump was at the center of a multi-step effort to overturn the election.