Former Rep. Denver Riggleman is joining the staff of the House select committee investigating the January 6 attack on the US Capitol, the third Republican that House Speaker Nancy Pelosi has added to the panel that GOP leadership has attacked as a partisan endeavor.

Riggleman -- a former Virginia congressman and Air Force intelligence officer who has been an outspoken critic of former  the rump -- will be a senior technical adviser for the committee, according to two sources familiar with the selection.

GOP Reps. Liz Cheney and Adam Kinzinger are the only Republican lawmakers serving on the committee, which held its first hearing late last month.

But as a former member, Riggleman brings a high profile, and his national security background will add additional legitimacy to the investigation.