Newly released internal Slack messages made public by Sen. Rand Paul, R-Ky., are renewing scrutiny over one of the most influential scientific papers published during the COVID-19 pandemic, with the communications indicating that several authors privately expressed greater uncertainty about the virus's origins than was reflected in their published conclusions, as reported by Fox News.

Paul released the messages Tuesday involving the authors of the March 2020 Nature Medicine paper, "The Proximal Origin of SARS-CoV-2."

The paper, written by Kristian Andersen, Robert Garry, Eddie Holmes and Andrew Rambaut, became one of the most frequently cited scientific publications addressing the origins of COVID-19 and was widely referenced by public health officials and news organizations as evidence against a laboratory origin.

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According to the released messages, however, some of the paper's authors privately acknowledged that they could not eliminate the possibility that the virus originated from a laboratory.

"The idea that it came from a lab is implausible, and yet, privately they're saying the opposite. … This level of dishonesty, I think, needs to be exposed," Paul told Fox News.

"These are people who get large, multimillion-dollar grants from our country, and we shouldn't be giving money to people who lied to us."

The internal discussions show Andersen assigning a 30% probability to a laboratory origin for SARS-CoV-2, while Holmes estimated the likelihood at 20% before later reducing that estimate to 10%.

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Those assessments differed from the paper's public conclusion that the virus had not been manipulated.

In one Slack message dated June 11, 2020, Andersen wrote:

"The part I’m really struggling with is that, at the end of the day, we really don’t have any hard evidence one way or the other — and especially given some of the recent evidence, we also can’t rule out that somebody actually put it in there."

He continued:

"That’s obviously not to say that somebody did, but we can’t rule it out. Our paper was pretty strong in saying ‘there’s no way,’ but I have less confidence in that statement at this stage."

The newly released documents also detail internal discussions surrounding the virus's furin cleavage site, a genetic feature that has remained central to debate over whether the virus emerged naturally or from laboratory research.

According to a news release from Paul's office, Andersen at one point told colleagues that "some smoking(ish) guns" had emerged, leaving him "not comfortable" and with "less confidence ... at this stage."

The communications further indicate that the authors coordinated with officials from the National Institutes of Health and members of the U.S. intelligence community while publicly defending the paper's conclusions.

Another subject discussed in the messages involved coronavirus researcher Ralph Baric.

While acknowledging his scientific expertise, the authors described a contentious professional relationship with Baric and expressed suspicions that he was the anonymous source they referred to as "Deep Throat," whom they believed leaked confidential peer-review information to a journalist.

According to the documents, the leaked material suggested the authors initially considered a laboratory origin before ultimately publishing different conclusions.

The release of the Slack messages follows another document disclosure by Paul on Monday.

Those records indicated that U.S. Customs and Border Protection agents had prepared to question British zoologist Peter Daszak after he returned from the World Health Organization's investigation into the origins of COVID-19.

According to the documents released by Paul, the FBI instructed CBP agents to stand down before questioning could take place.

The debate over COVID-19's origins has continued years after the pandemic began.

Last year, a scientific advisory group organized by the World Health Organization concluded that the pandemic most likely resulted from "zoonotic spillover," either directly from bats or through an intermediate host.

Meanwhile, Dr. Anthony Fauci, who led much of the federal government's public health response during the pandemic, is scheduled to testify before the Senate Homeland Security and Governmental Affairs Committee later this month after Paul, who chairs the committee, issued a subpoena.

Fauci has been accused by some of manipulating intelligence concerning the origins of COVID-19 and of lying to Congress regarding allegations tied to the pandemic's origins.

The upcoming hearing is expected to examine those issues alongside newly released records and other evidence gathered during the committee's investigation.

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