Former president Donald Trump attempted to call a member of the White House support staff who has been in talks with the House select committee investigating the Jan. 6, 2021, insurrection, according to people with knowledge of the attempt at contact.

Trump’s call was to a member of his support staff who worked with former White House aide Cassidy Hutchinson in some capacity and can corroborate aspects of her testimony, according to these people, who spoke on the condition of anonymity to discuss sensitive matters. The attempt at contact was considered unusual because this staffer had not spoken with the former president for some time.

The call from Trump to the staffer, who is still in public service, was revealed Tuesday by committee Vice Chair Liz Cheney, R-Wyo., at the end of the committee’s seventh hearing.

“After our last hearing, President Trump tried to call a witness in our investigation,” Cheney said. “A witness you have not yet seen in these hearings. That person declined to answer or respond to President Trump’s call and instead alerted their lawyer to the call.”

“Their lawyer alerted us and this committee has supplied that information to the Department of Justice,” Cheney added, without identifying the witness.

CNN first reported the role of the staffer. A Trump spokesman did not immediately respond to a request for comment.

Chairman Bennie Thompson, D-Miss., told reporters on Wednesday that the Justice Department must determine whether Trump’s call amounts to witness tampering. It is illegal to try to interfere with a witness’s testimony through either threats or promised rewards. Thompson said the committee would not reveal the person’s name.

“You know, we are concerned, obviously, about the witness. And we’re not going to put that witness in unnecessary jeopardy,” Thompson said.

Hutchinson offered bombshell revelations during her testimony, including that she was in the White House on Dec. 1, 2020, when a valet pointed her to “ketchup dripping down the wall” and a “shattered porcelain plate on the floor” of the dining room.

She said the valet told her that the president was “extremely angry … and had thrown his lunch.” The incident followed an interview then-Attorney General William Barr gave to the Associated Press in which he said the Justice Department had seen no evidence of systematic voter fraud.

Hutchinson also recounted a senior White House official telling her about a struggle between Trump and his Secret Service detail over whether he would be taken to the Capitol after his speech to protesters at the Ellipse on Jan. 6, 2021. And she testified that Trump had urged his supporters to march to the Capitol despite knowing some had come armed with weapons.

After Hutchinson’s public testimony on June 28, Cheney referenced two phone calls received by a witness – later revealed to be Hutchinson – that Cheney said raised “significant concern.”

“What they said to me is, as long as I continue to be a team player, they know I’m on the right team. I’m doing the right thing. I’m protecting who I need to protect. You know, I’ll continue to stay in good graces in Trump World,” Cheney, the committee’s vice chair, said the witness reported.

Trump has regularly called witnesses involved in the investigation, including former White House officials and campaign advisers, and has complained about the committee to a number of these people, said two people who have heard his comments.

In recent days, his advisers have tried to defend that practice, saying many of the people ensnarled in the investigation are also critical members of his political orbit.

Trump is a prolific worker of the telephone, sometimes making 50 to 100 calls a day in the White House, former administration officials said. He often used multiple cellphones, going around White House protocols and gatekeepers who would have preferred the calls come through a secure switchboard.

At one point, Trump asked an aide to buy him a cellphone because then-Chief of Staff John Kelly was trying to monitor his calls, former administration officials said.

The committee has continued to conduct its investigation behind closed doors, even as it prepares for a public hearing next Thursday that will focus on the 187 minutes in which a pro-Trump mob attacked the U.S. Capitol before Trump released a video calling on the rioters to go home.

Former Overstock CEO Patrick Byrne is expected to meet Friday with investigators. Byrne was present at the Dec. 18, 2020, meeting at the White House where Michael Flynn, Trump’s former national security adviser, and Sidney Powell, a pro-Trump lawyer, pushed Trump to seize voting machines and appoint Powell as a special counsel to assist his efforts to overturn the election results.

Rep. Adam Kinzinger, R-Ill., a member of the committee, has reiterated his interest in seeking an interview with former vice president Mike Pence and Trump. He told the Wall Street Journal in an interview that the panel could ultimately decide to try to compel Pence to testify by issuing the former vice president a subpoena.