In 2012, the Ukrainian prosecutor general Viktor Pshonka began investigating Ukrainian oligarch Mykola Zlochevsky, owner of the natural gas company Burisma Holdings, over allegations of money laundering, tax evasion, and corruption during 2010-2012.[33][34]
In 2015, Shokin became the prosecutor general, inheriting the investigation. The Obama administration and other governments and non-governmental organizations soon became concerned that Shokin was not adequately pursuing corruption in Ukraine, was protecting the political elite, and was regarded as "an obstacle to anti-corruption efforts".[22] Among other issues, he was slow-walking the investigation into Zlochevsky and Burisma and using the threat of prosecution to try to solicit bribes from Mr. Zlochevsky and his team – to the extent that Obama officials were considering launching their own criminal investigation into the company for possible money laundering.[33]
While visiting Kiev in December 2015, then-U.S. Vice President Joe Biden warned Ukrainian President Petro Poroshenko that, if he did not fire Shokin, the Obama administration was prepared to withhold $1 billion in loan guarantees. Biden later said: "I looked at them and said, 'I'm leaving in six hours. If the prosecutor is not fired, you're not getting the money.' [...] He got fired. And they put in place someone who was solid at the time."[35][36] Shokin was dismissed by Parliament in late March 2016.
In a sworn affidavit dated 4 September 2019[37], for a European court, Shokin testified that "On several occasions President Poroshenko asked me to have a look at the criminal case against Burisma and consider the possibility of winding down the investigative actions in respect of this company, but I refused to close this investigation."[38] Shokin wrote the affidavit in support of Ukrainian oligarch Dmytro Firtash.[39] John Herbst, the U.S. ambassador to Ukraine during the George W. Bush administration, said that Shokin's support of Firtash, who had been arrested for bribery in 2014, undercuts Shokin's claims to be motivated by transparency.[40][41]
Shokin claimed in May 2019 that he had been investigating Burisma Holdings.[29][42][43] However, Vitaly Kasko, who had been Shokin's deputy overseeing international cooperation before resigning in February 2016 citing corruption in the office, provided documents to Bloomberg News indicating that under Shokin, the investigation into Burisma had been dormant.[44][45]