Jason Dolan, a client of former President Donald Trump’s impeachment lawyer Michael van der Veen, on Wednesday pleaded guilty to conspiracy and obstruction of an official proceeding over the Jan. 6 riots at the U.S. Capitol.

Dolan, a Marine Corps veteran, was part of the largest conspiracy case put forward so far in the Jan. 6 prosecutions. Prosecutors allege that he was a member of the far-right group the Oath Keepers and conspired to block the congressional certification of the Electoral College results.