Feinstein on Tuesday released the full transcript of the committee's interview with Glenn Simpson, the co-founder of the opposition research firm that produced the explosive dossier detailing alleged ties between Trump and Russian Federation.
Several people familiar with the probe said Simpson's comments refer to a report from an Australian official who contacted US officials in late July with concerns about a conversation months earlier in London with Trump campaign adviser George Papadopoulos.
There has been no comment from the Federal Bureau of Investigation about Mr Simpson's testimony. That has angered Democrats, who say those charges are distractions from the Russian Federation investigations.
Notably, Simpson did not identify any other of the "pieces of intelligence" that the Federal Bureau of Investigation might have had to back up the dossier.
Mr Trump and some Republicans have attacked both Mr Simpson's firm and Mr Steele in recent months and also questioned the impartiality of the Federal Bureau of Investigation and the Justice Department in an apparent effort to discredit Mr Mueller's probe.
It may have been Trump campaign aide George Papadopoulos, who told an Australian diplomat that Russian Federation had "political dirt" on Hillary Clinton in May 2016, according to The New York Times. She can release the testimony of the committee that she is a member of on her own. Simpson said he had worked with Steele since 2009 and he is "basically a Boy Scout". "Like if you're a lawyer and, you know, you find out about a crime, in a lot of countries you must report that".
The FBI responded to Steele "by September", Simpson said, and Steele then met in mid- or late September with an FBI legal attaché in Rome. Steele and Simpson had previously contacted the FBI regarding material they had collected on the Trump campaign - a project with no other direct tie to the Clinton investigation. Look, they argued, the Donald Trump investigation was completely justified because the infamous "dossier", according to Simpson, had been corroborated by the FBI.
After the article was published, Simpson said, Steele severed his relationship with the Federal Bureau of Investigation.
"We've gotta count on Mueller being the only place that's going to ultimately get to the facts here", Murphy said.
"The dossier is, and continues to be, the subject of active investigations by Congress and intelligence agencies".
The dossier was written by a former British intelligence officer, Christopher Steele, under commission by the American political research shop Fusion GPS.
They have sued BuzzFeed, Fusion, Yahoo News and Steele. There's also an exchange in which Simpson says that neither he nor Steele asked for anyone's approval to go to the Federal Bureau of Investigation.
That inquiry ended in the spring 2016 but then another client engaged Fusion to conduct research on Trump.
"It's a false allegation", he said.
Meanwhile, President Trump's longtime personal attorney, Michael Cohen, has slapped Fusion GPS with a whopping $100 million defamation lawsuit for claiming he had colluded with Russian operatives despite easily disprovable "evidence".