One of the leading players behind the anti-Trump dossier claims the FBI had an informant inside the president's circle, and the secret source voluntarily fed information to the federal agency.

A lawyer for Fusion GPS Founder Glenn R. Simpson also claimed "somebody's already been killed as a result of the publication of this dossier."

The bombshells come from a newly released transcript of Simpson's interviews with members of Congress. On Aug. 22, Simpson spoke with Senate Judiciary Committee investigators for 10 hours.

Simpson had requested that his 312-page testimony be released. The ranking Democrat on the Senate Judiciary Committee, Sen. Dianne Feinstein, D-Calif., made Simpson's transcript public Tuesday.

TRENDING: Franklin Graham to lead prayer march in D.C.: 'Only hope for our country is God'

"The innuendo and misinformation circulating about the transcript are part of a deeply troubling effort to undermine the investigation into potential collusion and obstruction of justice," Feinstein said in a statement. "The only way to set the record straight is to make the transcript public."

As WND has reported, former British spy Christopher Steele compiled the anti-Trump dossier, which he said was given to the FBI "near the start of July." He had been hired by the Washington-based intelligence firm Fusion GPS, which funded Steele's research with cash from Hillary Clinton's campaign and the Democratic National Committee.

Simpson's testimony reveals FBI agents believed the information Steele provided. He said Steele told him the FBI had a source inside Trump's circle.

"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 organization," Simpson explained.

The inside source reportedly volunteered to provide information to the FBI, Simpson said, and was "someone like us who decided to pick up the phone and report something."

When Simpson was asked to identify the inside source, he said: "We had been really careful -- I was really careful throughout this process to not ask a lot of specific sourcing questions. There are some things I know that I just don't feel comfortable sharing because obviously it's been in the news a lot lately that people who get in the way of the Russians tend to get hurt."

Simpson said the inside source was independent of sources used for Steele's dossier.

The Clinton- and DNC-funded dossier contained some curious allegations from Russian government sources and was published on the anti-Trump website Buzzfeed, which admitted, "The allegations are unverified, and the report contains errors." The 35-page document included lewd allegations concerning Trump's personal life and claims regarding his purported financial ties to Russia.

Trump called the dossier "fake" and disputed all the allegations in it. Since the dossier was published, defamation lawsuits have been filed against Steele, Fusion GPS, former Wall Street Journal reporter Glenn Simpson, Buzzfeed, Huffington Post and Yahoo News concerning potentially libelous claims made in the document.

Despite the so-called "salacious and unverified" claims in the dossier, the FBI reportedly used the document to justify secretly monitoring Trump campaign adviser Carter Page and to bolster its Trump-Russia investigation, according to a CNN report published in April.

Just last week, Republicans Chuck Grassley, chairman of the Senate Judiciary Committee, and Lindsey Graham issued a criminal referral against Steele. They said the committee has reason to believe Steele lied to authorities about his discussions with the media concerning the dossier.

During his testimony, Simpson said Steele went to the FBI with his Trump-Russia findings because "he was very concerned about whether this represented a national security threat and ... he thought we were obligated to tell someone in government."

He continued, "he thought from his perspective there was ... a security issue about whether a presidential candidate was being blackmailed."

However, Steele stopped working with the FBI in the late stages of the 2016 presidential campaign, Simpson claimed, because he didn't believe the federal agency was taking his concerns seriously.

"I understand Chris severed his relationship with the FBI out of concern that he didn't know what was happening inside the FBI and there was a concern that the FBI was being manipulated for political ends by the Trump people," he said.

Asked if he verified Steele's sources and claims concerning Trump's alleged ties to Russia, Simpson declined to answer.

His lawyer explained: "It's a voluntary interview, and in addition to that he wants to be very careful to protect his sources. Somebody's already been killed as a result of the publication of this dossier and no harm should come to anybody related to this honest work."

It's unclear who the lawyer was saying had been "killed" because of the dossier's publication. However, the Sun reported in January 2017 that former KGB spy chief Oleg Erovinkin, a key source behind the dossier, was discovered dead in the back seat of his car in Moscow.

Simpson also discussed President Trump's taxes in his testimony.

"One of the things we found out was that, you know, when it comes to paying taxes, Donald Trump claims to not have much stuff," Simpson said. "At least the Trump organization. So they would make filings with various state and local authorities saying that their buildings weren't worth much."

He also indicated that Fusion GPS didn't manage to acquire Trump's tax documents.

"They were Trump properties and I believe we may have reviewed some public information about estate taxes and things like that," Simpson said. "We didn't have access to his tax returns."

Simpson said Fusion GPS found that Trump had "exaggerated" the worth of his real estate in legal filings, but there's nothing to indicate the exaggerations showed connections to Russia. He said the president's golf clubs aren't making much money.

"They were not profitable entities," he said. "I don't specifically recall. I just remember that these were not doing very well and that he'd sunk a lot of money into them and he hadn't gotten a lot of money back yet."

Simpson also said he had no "factual reason to believe" the meeting at Trump Tower between a Russian lawyer and Donald Trump Jr. was part of the Kremlin's effort to reach out to the Trump campaign.

"You know, as a sort of question of counterintelligence and just general investigation of Russian methods and that sort of thing, I think that's a reasonable interpretation," he said.