– Steve Bannon, President Donald Trump’s former chief strategist, will be interviewed by investigators working for the special counsel in the Russia investigation instead of testifying before a grand jury, according to a person familiar with the matter, a sign that Bannon is cooperating with the inquiry.

The special counsel, Robert Mueller, had subpoenaed Bannon to appear before a grand jury this week. But Bannon has agreed to cooperate with Mueller’s investigation and will be interviewed in the less formal setting of the special counsel’s offices in downtown Washington.

It was not clear why Mueller subpoenaed Bannon and did not first ask him to sit for an interview, as Mueller had done with more than a dozen current and former White House officials who were questioned in recent months. Mueller could still call Bannon to appear before a grand jury after he meets investigators.

Legal experts have said the subpoena could be a sign that the inquiry is accelerating, while others said it may have simply been a negotiating tactic to force Bannon to quickly agree to be interviewed.

The subpoena was served after Bannon was quoted in the new book “Fire and Fury: Inside the Trump White House” criticizing the president’s son Donald Trump Jr. and predicting that Mueller’s investigation will ultimately center on money laundering.

Bannon is still under subpoena from the House Intelligence Committee, which took the unusual step of subpoenaing him as he was being interviewed by its members Tuesday. He had refused to answer several questions about Trump, saying the White House had told him to assert executive privilege.

Committee members of both parties were angered by Bannon’s lack of cooperation during his 10 hours of testimony, and Democrats said that the White House had used executive privilege as a “gag order” to stop Bannon from talking about the president.

Lawmakers would like Bannon to return to Capitol Hill on Thursday to respond to questions he refused to answer.

Bannon lawyer Bill Burck relayed questions to the White House during the House interview. Bannon was told by the counsel’s office not to discuss his work on the transition or in the White House.