The whistleblower says his probe of Giuliani's ties to suspected Russian operatives was thwarted.

In July, Buma sent the Senate Judiciary Committee a 22-page statement full of eye-popping allegations, and the document leaked and was first reported last month by Insider (after a conservative blogger had posted it online). According to Buma’s account, Giuliani was used as an asset by a Ukrainian oligarch tied to Russian intelligence and other Russian operatives for a disinformation operation that aimed to discredit Joe Biden and boost Trump in the 2020 presidential race. Moreover, Buma says he was the target of retaliation within the bureau for digging into this.

Buma’s statement highlights Giuliani’s relationship with Pavel Fuks, a wealthy Ukrainian developer, who in 2017 hired Giuliani and paid him $300,000. Fuks once told the New York Times that he had retained Giuliani to lobby in the United States for the Ukrainian city of Kharkiv, where Fuks then lived. Giuliani has denied that he was paid to lobby for Kharkiv, insisting he only provided advice regarding security to the city. And Fuks has changed his tune. Through a spokesperson, he told Mother Jones that Giuliani’s work was limited to advising the city.

In his statement, Buma says that the FBI assessed Fuks to be a “co-opted asset” of Russian intelligence services, meaning a person who Russian intelligence used to advance its goals. Buma’s complaint does not name a specific Russian intelligence agency, but a person who spoke to agents involved in this investigation says that the FBI believes Fuks worked for the FSB, the successor to KGB. All this raises the possibility that Giuliani, a former Republican presidential candidate who became a close adviser to Trump, received a large payment directly from a Russian asset.

Buma alleges that Fuks has carried out various tasks for Russian spies, including laundering money for them. Fuks also reportedly paid locals to spray-paint swastikas around Kharkiv in the weeks before Russia’s invasion. Buma says Fuks did so to bolster Vladmir Putin’s claim that the invasion aimed to achieve the “de-Nazification of Ukraine.”