Senator Dianne Feinstein unilaterally released on Tuesday the transcript of a congressional interview with Glenn Simpson, whose research firm was behind the dossier on alleged contacts between Donald Trump's campaign and the Russian government.
Mr. Simpson has also spoken with investigators from the House and Senate intelligence committees, which have their own investigations into Russia's election interference.
By the time the FBI sat down in September 2016 for a full interview with the ex-British spy who had been researching Donald Trump's Russian Federation connections, the bureau had already received information raising concerns about possible collusion between the Trump campaign and Russian Federation, according to a transcript made public Tuesday.
"He thought from his perspective there was an issue - a security issue about whether a presidential candidate was being blackmailed", Simpson said.
Simpson said he didn't know whether the person was connected to the Trump campaign or a Trump company, adding that his understanding was the source was someone who had volunteered information to the Federal Bureau of Investigation or, in his words, "someone like us who made a decision to pick up the phone and report something".
Simpson told investigators that Steele is "basically a Boy Scout", saying he has worked with Steele on and off since 2009 and he knew him to be "a person who delivered quality work in very appropriate ways".
"My understanding was that they believed Chris at this point - that they believed Chris might be credible because they had other intelligence that indicated the same thing and one of those pieces of intelligence was a human source from inside the Trump Organisation", Mr Simpson said.
The New York Times reported last month that Papadopoulos told the Australian ambassador about the Russians' dirt on Hillary Clinton over drinks in London.
Feinstein released the testimony after the panel's Republican chairman, Charles Grassley, called on Friday for a criminal investigation into former British spy Christopher Steele. Chuck Grassley of Iowa, who had argued the committee needed to temporarily protect certain information while an investigation was ongoing. "Her action undermines the integrity of the committee's oversight work and jeopardizes its ability to secure candid voluntary testimony relating to the independent recollection of future witnesses, " said the spokesman, Taylor Foy. Republican-led committees are looking into whether the dossier was what led to the initial FBI investigation into whether the Trump campaign colluded with Russian officials in the 2016 election.
Last week Simpson, a former journalist, requested that the committee release the transcript in an op-ed in the New York Times, writing: "the public still has much to learn about a man with the most troubling business past of any United States president". "Feinstein for her courage", the research firm said in a statement.
Democrats says those investigations are a distraction.
Feinstein said she released the transcript to set the record straight.
In a statement, Fusion GPS said it "commends Sen".