Glenn R. Simpson, co-founder of the research firm Fusion GPS, arrives in November for a closed interview with the House Intelligence Committee. (Pablo Martinez Monsivais/AP)

The head of the research firm behind a dossier of allegations against Donald Trump said he tried to spur stories that the GOP candidate was under FBI investigation, because he was angry that then-FBI Director James B. Comey had reopened a probe into Hillary Clinton days before the 2016 election, according to a newly released transcript.

The interview of Fusion GPS co-founder Glenn R. Simpson was conducted behind closed doors in November with the House Intelligence Committee, which on Thursday released a transcript of the testimony. Sen. Dianne Feinstein (D-Calif.) released a transcript last week of the Senate Judiciary Committee's August interview with Simpson.

The dossier's origins have become a major point of contention in the political battles surrounding the ongoing special-counsel probe by Robert S. Mueller III into whether any Trump associates coordinated with Russia to interfere in the 2016 election.

The dossier, along with intelligence intercepts and a late-July warning from an Australian diplomat about a Trump campaign adviser, prompted the FBI to begin investigating several issues that involved the Trump campaign, according to people familiar with the matter.

Conservatives have repeatedly attacked the dossier as a politically motivated hit job that should not have triggered any investigation; Democrats have called such criticism a cynical ploy aimed at damaging the credibility of the FBI and Mueller's investigation.

In the new transcript, Simpson said he began talking to reporters in September and October 2016 about information that a British ex-spy named Christopher Steele had found that suggested Trump associates may have been conspiring with agents of the Russian government to sway the presidential race.

In the interview with the House committee, Simpson also discussed his concerns that Trump appeared to have connections to organized-crime figures. Trump has long denied those allegations and denounced the dossier's claims as lies.

Simpson said he had become alarmed about real estate deals involving Trump properties and wealthy Russians, and whether those interactions amounted to money laundering. Steele, who had been conducting the Russian-related research for Fusion GPS because of his prior intelligence work in Russia, had gone to the FBI in early July, warning them of what he thought were national security concerns involving Trump's alleged ties to Russia.

Simpson said that while their first conversations with reporters about the allegations took place in September and early October before the election, he didn't feel a sense of urgency about the issue because he still assumed Clinton would win the presidency.

But Simpson said he became alarmed when, in late October, Comey announced he was reopening the investigation into Clinton's use of a private email server while she served as secretary of state.

"We were shocked, and I felt, I mean, I guess I was angry," Simpson said. "At that point I felt like the rules had just been thrown out and that Comey had violated . . . one of the more sacrosanct policies, which is not announcing law enforcement activity in the closing days of an election."

Steele was "a little scared," Simpson said, "because he didn't really understand what was going on with the FBI."

As a result, Simpson said, "we began talking to the press again about — we decided that if James Comey wasn't going to tell people about this [Russia] investigation, that, you know, he had violated the rules, and we would only be fair if the world knew that both candidates were under FBI investigation."

Simpson said Steele was paid about $160,000 in total for his work as a subcontractor. Fusion GPS was hired in April 2016 by a lawyer representing the Democratic National Committee and the Clinton campaign, though the firm began its research into Trump in late 2015, working for a conservative website that was funded principally by a major GOP donor. After the Democrats hired Fusion GPS, the firm in turn hired Steele, Simpson said.

Simpson also acknowledged in the interview that he had done research on one other presidential candidate during the 2016 election cycle — Sen. Ted Cruz (R-Tex.).