Earlier this month, House Oversight Committee Chair James Comer, Republic-Kentucky, announced that a document in possession of the FBI that relates to Hunter and Joe Biden “has not been disproven and is currently being used in an ongoing investigation.”

In the hands of conservative media and some leading Republicans, that double negative quickly transformed into affirmative proof of a criminal bribery scheme involving the Ukrainian natural gas company that had hired Hunter while his father was vice president.

The idea that the charge has been proven is preposterous, but readers looking for details on the case have little place to turn outside of the conservative news outlets that have been making such claims. Yet if the FBI is telling Congress that it hasn’t disproved the allegation, it does raise serious questions: What exactly are the Bidens accused of doing? What is this document? And what has the FBI done to test the veracity of that evidence?

The charge is straightforward: If all the claims in the document are to be believed, a Ukrainian energy company, Burisma, funnelled $5 million to then-Vice President Joe Biden so that he would pressure Ukraine to fire the prosecutor investigating Burisma for corruption. Joe Biden did in fact successfully push the Ukrainian government to fire the prosecutor in March 2016, although as his defenders point out, getting the prosecutor fired was official US policy.

The evidence in question is a so-called FD-1023, which the FBI produces to memorialise a tip or some other information provided to the agency by a confidential human source or CHS. More or less anybody who walks into an FBI field office and provides information would have their claims documented in an FD-1023, which does not assess the credibility of the claim or otherwise couple it with analysis of existing information.

In May, an FBI whistleblower came forward to Sen Chuck Grassley, Republican-Iowa, alleging the existence of a damning FD-1023 involving Joe and Hunter Biden. Grassley made the claim public, but the FBI was initially reluctant to confirm the existence of the document. FBI Director Christopher Wray eventually did so.

The House Oversight Committee asked for a copy of the document and the FBI at first refused, saying releasing it to Congress would carry substantial risks but that members of Congress could view it in person at FBI headquarters.

“Revealing unverified or possibly incomplete information could harm investigations, prejudice prosecutions or judicial proceedings, unfairly violate privacy or reputations, create misimpressions in the public or potentially identify individuals who provide information to law enforcement, placing their physical safety at risk,” the FBI said in a statement. “Information from confidential human sources and members of the public is critical to the work of the FBI and we are also committed to protecting the confidentiality of anyone who comes forward.”

The FBI later compromised, allowing members of the committee to view the document on Thursday in a highly secure Capitol Hill room known as a SCIF (short for “sensitive compartmented information facility”), with additional opportunity to view it on Monday and Tuesday.

What we know about the document comes from public statements made by Grassley and Comer and leaks to the media, including The Intercept. The picture that emerges: The confidential human source reported to the FBI – which has reportedly deemed the source to be “highly credible” – in June 2020 that they had a conversation with a Ukrainian Burisma executive while Biden was vice president either in 2015 or 2016.

The executive asked the source for help linking Burisma up with an American energy company, and the CHS asked why their help was needed if the company had Hunter Biden, who sat on the company’s board. The executive said Biden was “dumb” – he was in the trough of addiction at the time – and that he had paid $5 million to Hunter Biden and $5 million to Joe Biden through a variety of accounts that would take years to disentangle.

Yet even if everything in the document is true, there is still an interpretation that would stop short of implicating Joe Biden: Hunter Biden could have been lying in order to extract more money from Burisma. The document does not (and cannot) answer the question of whether Hunter Biden told the company the truth about splitting the money with his father or whether it was a way to shakedown additional money and appear more influential than he was.

In that scenario, the Burisma executive would have believed he was bribing the vice president, yet his son would have pocketed the money. The Burisma executive reportedly told the CHS that he did not pay Joe Biden directly. He’d therefore have no way of knowing if Joe Biden got the money.

In the past, Hunter Biden has shared money with his father, including paying bills at Joe Biden’s Wilmington home. In a text message Hunter Biden sent to his daughter Naomi in 2019, he hinted at some type of arrangement. “I hope you all can do what I did and pay for everything for this entire family for 30 years,” Hunter Biden complained. “It’s really hard. But don’t worry, unlike pop, I won’t make you give me half your salary.”

A Daily Mail tabulation of the former vice president’s finances identified a $5.2 million discrepancy between his tax returns and public financial disclosures.

On the Senate floor on Monday evening, Grassley said that he had read the document with minimal redactions and that it contained a claim that the Burisma executive also kept 15 recordings of conversations with Hunter Biden and two with Vice President Joe Biden as “a sort of insurance policy for the foreign national in case that he got into a tight spot.”

The reference to the audio recordings, according to a source familiar with the document, is included in the version made available to Grassley, Comer and Democratic ranking member Jamie Raskin of Maryland, but was redacted in the version made available to the rank-and-file committee members.

On Tuesday, Wisconsin Sen Ron Johnson, a Republican who has played the most footsie with conservative conspiracy theories, tapped the brakes on the speculation around the audio tapes.

“That’s what this person says. But again, take that with a grain of salt. This could be coming from a very corrupt oligarch. He could be making stuff up,” Johnson said on conservative radio. “We don’t really know whether the tapes exist, we just really don’t know that [or] whether this was a bluff on whoever the executive was, we think it was Mykola Zlochevsky the CEO, the corrupt oligarch. But we really don’t know.”

In January 2020, Trump ally Rudy Giuliani shared a trove of information related to Hunter Biden with the FBI. The bureau referred those documents to the Western District of Pennsylvania, which had previously been assigned to handle any incoming election-related information. While taking initial steps to verify Giuliani’s information, a search of FBI records turned up previous FD-1023s from the CHS, which included allegations made in 2017 and 2018 that mirrored some of what was in Giuliani’s cache, according to a source on the House Oversight Committee.

The FBI then reached back out to the CHS to reinterview the source about their conversation with the Burisma executive, which produced the new FD-1023 in June 2020. The FBI has for years faced criticism over inadequate vetting of its confidential human sources.

• A Tell / The Intercept report