The January 6 committee is getting "significant cooperation with Team Pence," CNN reported.
Marc Short, former Vice President Mike Pence's chief of staff, is complying with a subpoena.
Trump banned Short from the White House after the January 6 insurrection.
The congressional panel looking into the January 6 insurrection is getting "significant cooperation from Team Pence," a source told CNN on Monday, with the former vice president's ex-chief of staff reportedly complying with the committee's investigation.
Marc Short, the Pence aide, could provide key testimony concerning both the lead-up to the attack on the US Capitol and events on January 6 itself to the committee, which is led by Rep. Bennie Thompson, a Mississippi Democrat, and Rep. Liz Cheney, a Wyoming Republican.
As Insider previously reported, Short was critical of the legally dubious effort, spearheaded by right-wing attorney John Eastman, to have Pence block the certification of President Joe Biden's victory in the 2020 election.
One constitutional law expert described the plan as a "proposed coup cloaked in legal language." Short himself called it "boneheaded analysis."
Eastman, by contrast, has refused to comply with the investigation by the House select committee, recently invoking his 5th Amendment right to remain silent.
Short was with Pence on January 6 when a mob of former President Donald Trump's supporters ransacked Congress in an effort to block Biden's victory, some of them demanding that Pence be executed for declining to do so himself.
After the attack, Trump barred Short from the White House.
A spokesperson for the committee did not immediately respond to Insider's request for comment.