President Donald Trump’s personal lawyer, Rudy Giuliani, attempted to secure a visa from the State Department for ousted Ukraine prosecutor Viktor Shokin, diplomat George Kent told congressional investigators this week, according to two people familiar with his deposition.

Kent spoke Tuesday behind closed doors to House investigators spearheading the formal impeachment inquiry against Trump.

The visa request story was first reported Friday by CNN.

Shokin, fired in 2016 following an international campaign for his ouster that included the support of then-Vice President Joe Biden, helped Giuliani form the basis of an unproven story that he was let go at the say so of the former vice president to thwart any corruption inquiries into his son's work in Ukraine.

Deputy Assistant Secretary of State George Kent leaves Capitol Hill after testifying before congressional lawmakers as part of the House impeachment inquiry into President Donald Trump, on Tuesday. Andrew Harnik / AP

Hunter Biden worked on the board of Ukranian energy firm Burisma from 2014 to 2018. No wrongdoing on his part or on the part of his father has been proven.

But the theory that the former vice president intervened in Ukraine on behalf of his son has been repeated by Trump, who could face off against Joe Biden in the 2020 election.

It’s unclear when Giuliani requested the visa, but he and associates Igor Fruman, Lev Parnas and George Boyle interviewed Shokin by phone Jan. 23, according to documents the Intelligence Community Inspector General Michael Atkinson gave to Congress and obtained by NBC News.

Two days later, on Jan. 25, Giuliani and associates interviewed Shokin’s successor, Yuriy Lutsenko, in person at Giuliani’s Manhattan office, according to the same documents.

Viktor Shokin in 2016 in Ukraine. Gleb Garanich / Reuters file

The information from those interviews was the basis of Giuliani’s claims that Joe Biden pressed Ukraine to fire Shokin, Ukraine’s general prosecutor, because Shokin was investigating the energy company whose board Hunter Biden sat on.

Fruman and Parnas were arrested last week on suspicion of conspiracy, making false statements to the Federal Election Commission and falsification of records in connection with an alleged attempt to influence U.S. politicians and government officials.

Boyle, a former New York Police Department detective, works for the firm Giuliani Partners.