"We look at all cases that were closed down or which were divided into separate cases, in order to be able to make a decision on whether it was illegal," says prosecutor Ruslan Ryabosjapka.

The authorities have previously stated that the investigation of the company Burisma focuses on a period before Hunter Biden became a board member.

- Work will continue and we will tell you about the results later, says Ryabosjapka.

Hunter Biden has been at the center of major politics since President Donald Trump called on Ukrainian President Volodymyr Zelenskyj to investigate Joe Biden and Hunter Biden's business in Ukraine. Trump has also called on China to investigate Biden. According to NBC, it is likely a journey that Joe and Hunter Biden undertook when Joe Biden was vice president. Hunter Biden then met a banker in China when he opened a venture capital fund.

The issue is politically explosive because Joe Biden is a candidate for running for the 2020 Democratic presidential election, and could thus become the main opponent of President Trump's Republican Party.

Trump doesn't want to answer

The scandal has led to a state investigation against Donald Trump, which is being investigated for suspicions that he has condemned an investigation of Joe and Hunter Biden with $ 400 million (equivalent to about $ 4 billion) in military support to Ukraine.

On Friday, Trump did not want to answer a direct question whether he intends to cooperate with the investigation.

"I don't know, it's up to the lawyers," Trump said at a White House press conference.

Donald Trump, who describes the investigation as a coup, has repeatedly denied that he offered anything in exchange for an investigation by Joe and Hunter Biden.

But the Congressional Intelligence Committee has published text messages from US diplomats, where at least one of them was aware that they exerted "additional pressure on Ukraine to deliver on the president's demand that Ukraine initiate politically motivated investigations," according to Democrats leading the judicial inquiry.

Raging against Trump

The Democrats are in the majority in the House of Representatives who decide whether to initiate a judicial process. The Senate, where the Republicans have taken over, makes the final decision whether Donald Trump should be forced to resign.

Republican Senator Mitt Romney is furious with Trump:

"The President's shameless and unprecedented call to China and Ukraine to investigate Joe Biden is unfair and terrible, of all things to judge," Romney writes on Twitter.

"When the only American citizen that President Trump selects for China's inquiry is his political opponent in the midst of the Democrats' nomination process, it is credible to suggest that it is anything but politically motivated," he writes.