Ukraine intends to fire the prosecutor who spearheaded investigations into the natural gas firm that employed former Vice President Joe Biden's son and who compiled a dossier that accused him of corruption.

Kostiantyn Kulyk, who was a deputy to former Prosecutor General Yuriy Lutsenko, failed to show up for a mandatory legal exam last month and did not file an official justification for being absent, a source told Reuters. His dismissal is expected to take place by Dec. 31.

The new prosecutor general, Ruslan Ryaboshapka, instituted the written exam for all employees of the General Prosecutor’s Office under President Volodymyr Zelensky, who took office in May, as part of an effort to overhaul a system with a reputation for political retribution.

Already more than 400 prosecutors, a third of the staff, have been fired for refusing to take the skills exam that some have criticized as being unfair. Among those fired were 13 prosecutors from the Special Investigations Unit who oversaw corruption cases that stem back to former President Viktor Yanukovych. Two of those inquiries involved former Trump campaign chairman Paul Manafort.

Kulyk was in charge of the criminal case looking into Burisma Holdings, a natural gas firm owned by a Ukrainian oligarch and is a controversial figure in Ukraine who has been accused of conducting politically motivated criminal cases. He was indicted on charges of illegal enrichment in 2016 and faces scrutiny for his ties to Yevhen Zhylin, a man in eastern Ukraine accused of working as a Russian intelligence agent.

Hunter Biden, the 49-year-old son of the former vice president, earned $50,000 per month to serve on Burisma's board from 2014 to 2019. His role at Burisma became fodder for President Trump and his allies to accuse the elder Biden, a leading 2020 Democratic candidate for president, of pushing Ukraine in 2016 to fire then-Prosecutor General Viktor Shokin to stop him from investigating Burisma.

Trump's efforts to pressure Ukraine to investigate the Bidens, as evident in a July 25 phone call with Zelensky, have become central to an impeachment investigation looking into Trump's possible abuse of power.

Kulyk, who reportedly compiled a seven-page dossier on Biden's business dealings, has said former U.S. Ambassador to Ukraine Marie Yovanovitch, a witness in the impeachment proceedings, blocked his efforts to provide evidence to the FBI by denying him a visa. Trump's personal lawyer Rudy Giuliani said he later met Kulyk to discuss the Bidens.

Joe Biden has accused Giuliani of spreading “false, debunked conspiracy theories” about him as he seeks the White House.