"The primary concern of the US government since 2014 was Burisma's owner -- Mykola Zlochevsky -- whose frozen assets abroad we had attempted to recover on Ukraine's behalf," Kent said.
"In early 2015, I raised questions with the deputy Prosecutor General about why the investigation of Zlochevsky had been terminated, based on our belief US Diplomatthat prosecutors had accepted bribes to close the case."
The impeachment inquiry, which began after a US intelligence community whistleblower, filed a confidential internal complaint that came to light when the White House tried to block Congress from seeing it.
The whistleblower's complaint at the heart of the House's inquiry alleges that Trump pushed Ukraine to investigate Joe Biden, the former Vice President's son and the 2016 election in order to help the President politically and that the White House took steps to cover it up. Trump has denied doing anything improper.
Trump has pushed an unproven accusation that then Vice President Biden improperly tried to help his son by pressuring the Ukrainian government to fire the country's prosecutor general. Hunter Biden served on the board of the Ukrainian natural gas company at the time.
There is no evidence of wrongdoing by either Joe or Hunter Biden in Ukraine.