Ukraine’s new top prosecutor announced he will open a review into the criminal proceedings dismissed against Burisma Holdings, an oil and gas conglomerate with ties to Joe Biden’s youngest son, Hunter.

Ruslan Ryaboshapka, Ukraine’s newly appointed prosecutor general, announced at a press conference on Friday that his office will review 15 prior cases that were closed under suspicious circumstances by his predecessor.

“We are now reviewing all the cases which were closed, fragmented or investigated earlier in order to make a decision on cases where illegal procedural decisions were taken,” Ryaboshapka said.

The news comes only days after Ukraine announced it was opening a public corruption investigation into Yuriy Lutsenko, the country’s most recent prosecutor general. Lutsenko, who served a prison sentence for embezzlement and corruption in the mid-2000s, was appointed to the post in 2016 after Joe Biden demanded the ouster of his predecessor. The incident in question and the Biden family’s ties to Burisma are the center of the impeachment inquiry House Speaker Nancy Pelosi launched last month.

The controversy began when President Donald Trump suggested the Ukrainian government investigate Hunter Biden’s tenure on Burisma’s board of directors. Hunter Biden had joined the company in 2014, purportedly making as much as $83,000 per month, to consult on legal issues. The appointment immediately raised questions from ethics watchdogs in both the U.S. and Europe about the true nature of his role, since he possessed no background in either the energy industry or Ukraine.

Around the same time Hunter Biden joined Burisma, his father was appointed as the Obama administration’s point man on Ukraine. Even more troubling is that at the time of the appointment, Burisma was attempting to sway western leaders after its founder, Mykola Zlochevsky, was accused of money laundering and had his assets seized in Great Britain. Zlochevsky is rumored to be one of eastern Europe’s leading oligarchs and has strong political ties to former Ukrainian President Viktor Yanukovych — a staunch ally of Russian President Vladimir Putin.

In 2015, Viktor Shokin, who was then the prosecutor general, led the first investigation into Zlochevsky and Burisma. It is uncertain if the probe extended to Hunter Biden, although Shokin has recently admitted that prior to his ouster he was warned to back off the matter. Regardless, Shokin never got to complete the probe, thanks to the former vice president’s intervention.

Biden, who has publicly bragged about the firing, reportedly threatened to withhold more than one billion dollars of U.S. aid if the Ukrainian government did not remove Shokin. The former vice president has claimed the demand came from then-President Barack Obama, who had allegedly lost faith in the prosecutors’ ability to tackle corruption. Regardless of the reason, Lutsenko dropped the investigation into Burisma and Zlochevsky during his tenure, allowing the oligarch to return to the country after having fled it in 2014.