Kremlin operatives used the notorious anti-Trump dossier to “settle scores” and arrest and kill possible U.S. intelligence informants, the co-founder of the Washington private intelligence firm that commissioned the report has told a congressional panel.

“There was a series of episodes where people were arrested or died mysteriously that came shortly after the disclosure of the existence of this information,” Fusion GPS co-founder Glenn Simpson told the House Intelligence Committee’s late last year. “To my knowledge, it wasn’t anyone that helped us. [I] think it was more likely people who were taking the opportunity to settle scores or were falsely accused.”

Late Thursday, House Republicans released the transcript of their interview with Mr. Simpson, just a week after Democratic Sen. Dianne Feinstein published the Senate’s session with the opposition researcher and former Wall Street Journal reporter.

While doubts about Mr. Simpson’s credibility have swirled for months, his 165-page House testimony in November offered fresh clues into the numerous controversies the dossier has created.

Also Thursday, White House communications director Hope Hicks’s scheduled appearance before the House panel’s probe of Russian meddling in the 2016 election was being delayed amid questions of executive privilege and what she would agree to talk about, CNN reported.

Initially hired by a conservative website, Fusion GPS switched to the Democratic National Committee and lawyers working for Democratic nominee Hillary Clinton, who funded the dossier compiled by onetime British intelligence agent Christopher Steele.

Republicans have charged that finding in the unverified dossier had been misused to justify the launch of the FBI’s investigation into the Trump campaign, and eventually led to the appointment of special counsel Robert Mueller.

In the testimony released Thursday, Mr. Simpson sidestepped questions about the dossier’s funding. He did, however, reveal that Fusion GPS paid Mr. Steele about $160,000 for his work.

Asked about the credibility of Mr. Steele’s findings, he was curt: “Chris is the spy. I am the ex-journalist so I defer a lot to his professionalism,” Mr. Simpson said.

Thursday’s move by the House Intelligence Committee to make public their Simpson interviews came on a unanimous vote.

Sources close to the committee were quoted as saying that the move was an effort by committee Republicans to thwart the panel’s leading Democrat, California Rep. Adam Schiff, from making it seem as if they were trying to keep the testimony a secret.

Earlier this week, Mr. Schiff called for the release of the transcript.