Washington (AFP) – A former top White House aide with unique access to Donald Trump and inner workings of the West Wing was expected to testify publicly Tuesday before the committee probing the attack on the US Capitol.

Cassidy Hutchinson, an executive assistant to Trump's chief of staff Mark Meadows, was a central figure in the White House around the period of the insurrection on January 6 last year.

She has already been the source of several blockbuster revelations, appearing in videotaped depositions at two previous hearings and memorably naming a group of House Republicans who sought pardons from Trump following the violence.

She was also in contact with officials in the battleground state of Georgia, where Trump infamously pressured officials to “find” enough votes to overcome Joe Biden's victory margin in a phone call that is the subject of a criminal probe.

Hutchinson testified behind closed doors in February, March and May, revealing she saw Meadows incinerate documents in his office after meeting a Republican congressman implicated in the plot to overturn the election.

The lawmaker, Scott Perry, was pivotal in Trump's failed effort to install his own pliant attorney general as part of a plan to co-opt the Justice Department into his scheme to cling to power.

It was Hutchinson, according to CNN, who told the select committee that Trump voiced approval for the “hang Mike Pence” chants from rioters at the Capitol — an allegation that was among the many eye-popping claims to come out of the opening hearing on June 9.

Hutchinson also testified that she remembered a Secret Service agent informing Meadows of intelligence reports saying there could potentially be violence on January 6.

‘Public spirit'

“I don't know what Cassidy Hutchinson will say today,” conservative political commentator Bill Kristol, a founder of the advocacy group Defending Democracy Together, posted on Twitter. 

“But by agreeing to step forward and testify under oath, this young woman is showing far more public spirit, integrity and courage than many of her well-established elders who have chosen a far easier and less honorable path.”

Meadows himself has refused to testify before the panel since handing over thousands of text messages and other documents in the early stages of the investigation.

The House of Representatives held Meadows in contempt in December but the Justice Department decided not to charge him.

The announcement of Tuesday's hearing with less than 24 hours' notice raised eyebrows across Washington, since the committee had said it was pushing the rest of its hearings to July and perhaps beyond.

The panel revealed the about-face in a brief release which didn't mention the purpose of the hearing or reveal who would appear, simply saying it would “present recently obtained evidence and receive witness testimony.”

The reason for the change of plan remained a mystery hours ahead of Hutchison's appearance, although US media reported she had become more cooperative since changing lawyers earlier this month.

Congressional media outlet Punchbowl reported that there had been “sincere concerns” about Hutchinson's safety because of what she knows and has already revealed.

The committee did not say if there would be more than one witness and Washington insiders speculated that documentary filmmaker Alex Holder's footage of Trump and his family could also figure.

Meanwhile, Trump lawyer John Eastman, the architect of the former president's scheme to overturn the election, revealed in a court filing Monday that the FBI had seized his cell phone. 

He said he was confronted by FBI agents as he was leaving a restaurant and called for a judge to have his phone returned.