Jared Kushner, Donald Trump's son-in-law and adviser, testified Thursday before a House investigation committee tasked with shedding light on the attack by thousands of supporters of the former US president on the Capitol building last year.

Ivanka Trump's husband, Jared, was Trump's closest advisor and the first member of his family to testify before the committee.

Jared spoke via video link after voluntarily agreeing to answer the committee's questions without receiving a summons.

On January 6, 2021, numbers of Trump supporters attacked the headquarters of Congress in an attempt to disrupt the process of confirming the victory of Joe Biden in the presidential elections that took place in January 2020.

On that day, Kushner, in charge of sensitive files such as the Middle East peace process, was returning from a trip to Saudi Arabia and had not spent the night in the White House.

Kushner's testimony concludes a week of press leaks about the months prior to the attack that shook the foundations of American democracy.

Elaine Luria, a member of the investigative committee, told MSNBC that Kushner "was able to provide us with information voluntarily, to verify and prove his point" about the election.

Speaking with him "was really helpful," she added.

Conservative activist Virginia Thomas, wife of Chief Justice Clarence Thomas, sent more than two dozen letters between November 2020 and January 2021 to Donald Trump's chief of staff, Mark Meadows, imploring him to block Biden's victory announcement.

The media also revealed a loophole for about eight hours in the phone records that Trump made from the White House on January 6, 2021, specifically during the period when his supporters stormed the Capitol Building.

The committee indicated that Trump may have used unofficial communication channels such as prepaid phones whose communications cannot be traced, which the former president vehemently denied.

The committee would also like to hear from Ivanka Trump, who was in her father's first circle of advisers and was in the White House on the day of the attack on Congress, and the media reports that she begged her father to denounce the violence.

The Biden administration said Tuesday that it was refusing to guarantee Jared Kushner and Ivanka Trump "executive powers" that would allow some communications between the president and his advisers to be kept secret.

The commission is about to release the findings of the investigation and plans to hold public hearings in the spring.

The Washington Post reported that the Justice Department, which is also investigating the attack that killed at least five people, "has expanded (its investigations) to include preparations for the election rally" that Trump held before the violence, including everyone who "helped to plan, finance and organize it."