A former senior White House employee with unrivaled access to Donald Trump and the inner workings of the West Wing was scheduled to speak publicly before the committee investigating the attack on the US Capitol on Tuesday.

Cassidy Hutchinson, an executive assistant to Trump's chief of staff Mark Meadows, was a key player in the White House during the January 6 insurgency.

More than 775 people have been arrested in connection with the Capitol attack. Some 280 have been charged with obstructing an official proceeding.

See this: Jan.6: Who do Americans hold responsible? 

She has previously been the source of some explosive discoveries, having appeared in filmed depositions at two prior sessions and identified a number of House Republicans who requested pardons from Trump in the aftermath of the violence.

She also spoke with authorities in Georgia, where Trump famously urged officials to "find" enough ballots to overcome Joe Biden's winning margin in a phone call that is the subject of a criminal investigation.

Hutchinson testified behind closed doors in February, March, and May, claiming that she witnessed Mark Meadows incinerate documents in his office after meeting with a Republican lawmaker implicated in the election-rigging conspiracy.

Read more: Trump's aide may face prosecution for refusing to testify for Capitol Riots

According to CNN, Hutchinson told the select committee that Trump approved of rioters' "hang Mike Pence" cries at the Capitol, a charge that was among the numerous eye-popping assertions made during the first hearing on June 9.

Hutchinson also testified that she recalls a Secret Service person warning Meadows about intelligence inputs indicating the possibility of violence on January 6.

Meadows has declined to appear in front of the panel after giving up hundreds of text conversations and other evidence early in the probe. 

According to the Congressional media site Punchbowl, there have been "sincere concerns" regarding Hutchinson's safety as a result of what she knows and has already stated.

The committee did not specify if there would be more than one witness, but Washington insiders thought that documentary director Alex Holder's video of Trump and his family may be used.

The FBI seized the phone of former President Donald Trump's election attorney John Eastman last week, as per a new court filing from the conservative lawyer.

Eastman revealed the search and seizure in federal court in a lawsuit filed in New Mexico on Monday aiming at having his phone returned.