The 312-page transcript shows that Republican staffers on the committee repeatedly pressed Simpson about whether he had political motivations in hiring Steele.
The Steele dossier - which became public in January 2017 - was drawn together after an investigation funded by Republicans trying to block Mr Trump from becoming the party's presidential candidate.
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.
Eventually, Fusion GPS hired Christopher Steele, a former British spy who had worked in Russian Federation in the 1990s, to reach out to his sources there.
Rather than limit the debate on the issue, Feinstein opened up information previously unknown to the American people.
Simpson said he didn't know whether the person was connected to the Trump campaign or a Trump company, adding that his understanding was that the source was "someone like us who chose to pick up the phone and report something".
"Crooked Hillary" and "Pocahontas" are now joined by "Sneaky Dianne Feinstein", who Trump described as "underhanded" for disclosing details behind a controversial dossier allegedly tying the president to Russian Federation during his campaign.
This means the FBI divulged information about an ongoing investigation to Steele.
The Fusion GPS lawsuit, which was filed at a federal court level, seeks $100 million in damages.
"Somebody's already been killed as a result of the publication of this dossier", Levy said.
Cohen also filed a separate suit against Fusion GPS, the research firm that was behind the document. The anti-Trump dossier was paid for by Hillary Clinton's campaign and the Democratic National Committee.
The special counsel's team of investigators has expressed interest in speaking with Trump, but no details have been worked out.
Trump has a long history of anti-Jewish controversies. That decision marks the most serious break yet in the once cooperative relationship she has had with the Republican chairman of the committee, Senator Charles E. Grassley of Iowa.
She continued, "And I think in these hearings more should be released than held back, because when you hold something back it gives all of the people who have an axe to grind an opportunity to grind that axe to a fine edge, and they do".
They have raised questions about whether the Federal Bureau of Investigation may have relied on the Steele document to improperly obtain surveillance warrants to spy on Mr Trump's campaign associates.
On Tuesday, Sen. Chris Coons, D-Del., a member of the Judiciary Committee, told reporters that Feinstein's release of the Simpson transcript would mark "the end of bipartisan cooperation" on the panel.
Through much of 2017, Feinstein and Grassley made joint requests for information about Russian Federation and the FBI's investigation of election interference.