The former White House press secretary Stephanie Grisham told the House select committee investigating the Capitol attack that Donald Trump hosted secret meetings in the White House residence in days before 6 January, according to two sources familiar with the matter.

The former senior Trump aide also told House investigators that the details of whether Trump actually intended to march to the Capitol after his speech at the Ellipse rally would be memorialized in documents provided to the US Secret Service, the sources said.

The select committee’s interview with Grisham, who was Melania Trump’s chief of staff when she resigned on 6 January, was more significant than expected, the sources said, giving the panel new details about the Trump White House and what the former US president was doing before the Capitol attack.

Grisham gave House investigators an overview of the chaotic final weeks in the Trump White House in the days leading up to the Capitol attack, recalling how the former president held off-the-books meetings in the White House residence, the sources said.

The secret meetings were apparently known by only a small number of aides, the sources said. Grisham recounted that they were mostly scheduled by Trump’s chief of staff, Mark Meadows, and that the former chief usher, Timothy Harleth, would wave participants upstairs, the sources said.

Harleth, the former director of rooms at the Trump International Hotel before moving with the Trumps to the White House in 2017, was once one of the former first family’s most trusted employees, according to a top former White House aide to Melania Trump.

But after Harleth sought to ingratiate himself with the Biden transition team after Trump’s defeat in the 2020 election in order to keep his White House role, Trump and Meadows moved to fire him before Melania Trump stepped in to keep him until Biden’s inauguration.

Grisham told the select committee she was not sure who exactly Trump met with in the White House residence, but provided Harleth’s name and the identities of other Trump aides in the usher’s office who might know of the meetings, the sources said.

The Guardian previously reported that Trump made several phone calls from the Yellow Oval Room and elsewhere in the White House residence to lieutenants at the Willard hotel in Washington the night before the Capitol attack, telling them to stop Joe Biden’s certification.

Trump increasingly retreated to the White House residence to conduct work as his presidency progressed, according to another former Trump administration official, as he felt less watched by West Wing aides than in the Oval Office.

Towards the end of his presidency, the former Trump administration official said, an aide to former White House adviser Peter Navarro tried at least once to quietly usher into the residence Sidney Powell, a lawyer pushing lies about election fraud, to speak with Trump.

A spokesperson for the select committee declined to comment on Grisham’s interview that took place the first week of January. Harleth did not respond to questions about the meetings in the White House residence when reached last week by phone.

Over the course of her hours-long interview, Grisham told House investigators that the mystery surrounding Trump’s promise at the Ellipse rally that he would march with his supporters to the Capitol might be resolved in Trump White House documents, the sources said.

The former president’s purported intention to go to the Capitol has emerged as a crucial issue for the select committee, as they examine whether Trump oversaw a criminal conspiracy coordinating his political plan to stop Biden’s certification with the insurrection.

Trump’s promise is significant as it served as one of the primary motivations for his supporters to march to the Capitol alongside militia groups like the Oath Keepers, and was used by far-right activists like Alex Jones to encourage the crowd along the route.

But Trump never went to the Capitol and instead returned to the White House, where he watched the attack unfold on television – after being informed by the Secret Service before the insurrection that they could not guarantee his security if he marched to the Capitol.

The select committee is now trying to untangle whether Trump made a promise that he perhaps had no intention of honoring because he hoped to incite an insurrection that stopped the certification – his only remaining play to get a second term – one of the sources said.

Grisham told the select committee that Trump’s intentions – and whether the Secret Service had been told Trump had decided not to march to the Capitol – should be reflected in the presidential line-by-line, the document that outlines the president’s movements, the sources said.

The chairman of the select committee, Bennie Thompson, has told reporters the panel is already seeking information from the Secret Service about what plans they had for Trump on January 6, as well as what evacuation strategies they had for then-vice president Mike Pence.

But the presidential line-by-line, which gets sent to the Secret Service, could also reveal discussions about security concerns and suggest a new line of inquiry into why an assessment about conditions that were too dangerous for the president were not disseminated further.

Grisham also told the select committee about the necessary coordination between the Trump White House, the Secret Service and organizers of the “Save America” rally at the Ellipse on 6 January in order to ensure Trump’s appearance, the sources said.

The former Trump aide suggested to the select committee that Trump was determined to speak at the rally once he heard about its existence, the sources said, and was constantly on the phone to oversee the event’s optics, the sources said.