KYIV — A court ruling in Ukraine has forced state investigators to open a probe into alleged pressure by then-Vice President Joe Biden that led to the 2016 dismissal of Viktor Shokin as the country’s prosecutor general, officials said Thursday.

President Donald Trump last year pressed Ukraine President Volodymyr Zelensky for an investigation of this kind, leading to Trump’s impeachment by the House and his eventual acquittal in a Senate trial.

Shokin’s firing, however, was not a unilateral action directed by Biden. It was prompted by a push for anti-corruption reforms developed at the State Department and coordinated with the European Union and the International Monetary Fund.

Shokin’s lawyer, Oleksandr Teleshetsky, said the probe was launched in response to a court order, after an appeal for action by Shokin. The State Bureau of Investigations confirmed a case was opened.

Trump and his allies have put intense pressure on Zelensky’s administration to open investigations into Joe Biden, and his son Hunter Biden who sat on the board of a Ukrainian gas company Burisma.

From late 2018 Shokin met with Trump’s personal attorney, Rudy Giuliani, as Giuliani sought political dirt on the Bidens. Shokin has long been angered by what he sees as an unfair dismissal following foreign pressure.

Shokin has claimed he was pushed out by Biden because he tried to launch a probe into Hunter Biden’s role at Burisma. In fact, Ukrainian investigations into Burisma related to the period before Hunter Biden joined the board.

“They need to investigate this. They have no other alternative. They are required to do this by the decision of the court. If they don’t, then they violate a whole string of procedural norms,” Teleshetsky said in an interview.

Shokin’s January appeal to the court mentioned Joe Biden by name, but the case opened by the SBI mentions only a U.S. citizen, Teleshetsky said.

Daria Kaleniuk, director of Ukraine’s Anti-Corruption Action Center, said that under Ukrainian law, anyone could go to court and demand that the SBI open a case. If a court approved it, the SBI was required by law to do so, even if officials did not believe there was enough evidence.

“The fact that it was opened after a decision of the court indicates that first the SBI didn’t open this case, but the attorneys of Shokin made the SBI open this case,” she said.

“Let’s say I can write a claim to the SBI that I think aliens stole my car,” she continued. “And the SBI obviously will not open [a case] as there is not evidence of a crime. But then I can go to court and make the SBI open it, through a court decision. So this case looks to me like that.”

She said it was possible for the case to lie dormant in the system for years.

“If I was a SBI investigator, I would close that case immediately,” she said.

When he was vice president, Biden urged Ukraine authorities to sack Shokin, citing his failure to act against corruption, concerns shared by other Western nations. In 2015 Biden warned Ukrainian authorities that the country could lose around $1 billion in loan guarantees unless Shokin was removed.

Biden is one of a narrowing field of Democrats contending to be the party’s presidential candidate, although Sen. Bernie Sanders, I-Vt., has emerged as the front-runner.

Shokin was dismissed in March 2016 after just over a year in office by the then Ukraine president, Petro Poroshenko, who was close to the prosecutor and acted reluctantly.

Shokin would become a key figure in efforts by Trump and his allies to press Ukraine to carry out investigations into Biden.

When Trump spoke to Zelensky in a July 25 phone call, he appeared to praise Shokin and call his removal unfair.

“I heard you had a prosecutor who was very good and he was shut down and that’s really unfair,” Trump told Zelensky, according to a rough transcript.

At the heart of Trump’s impeachment trial was his move to freeze military aid to Ukraine shortly after the July conversation. At the same time, Ukrainian officials were seeking a prized White House meeting between Zelensky and Trump. Zelensky has repeatedly stated he felt no pressure from Trump to establish investigations into Biden.

Secretary of State Mike Pompeo met Zelensky in January in Kyiv and denied that the Trump administration ever demanded the investigation as a condition for a White House meeting between Trump and Zelensky.

But Pompeo did not offer a date for an Oval Office meeting, saying simply, “We’ll find the right time.”

Since that meeting, Zelensky has appointed a new chief of staff Andriy Yermak, who has closer ties with Trump allies such as Giuliani.

Ukrainian prosecutor general Ruslan Ryaboshapka said in October that prosecutors would audit the all previous cases related to Burisma. At the time, Ryaboshapka said he saw no evidence of wrongdoing by Hunter Biden who joined the board in 2014.

“We are now reviewing all proceedings that were closed, fragmented or investigated earlier, in order to make a decision in cases where illegal procedural decisions were made and to review them,” Ryaboshapka, adding that these cases focused on the time before Hunter Biden was on the board.