Calling former Vice President Joe Biden's denials of knowledge about his son's business dealings "patently ridiculous," author Peter Schweizer said Thursday on "America's Newsroom" that Hunter Biden's role on the board of a Ukrainian gas company must be investigated.

Schweizer, the author of “Secret Empires" and president of the Government Accountability Institute, argued it's "legitimate" for Biden and his son to be probed because Biden was vice president at the time.

"The notion that if you're running for office, you get a 'get out of jail free' card, I think, is ridiculous. There's nothing wrong with saying it should be done through the Department of Justice, working with Ukrainians," he said.

Anchor Bill Hemmer asked Schweizer about a FoxNews.com report that the fired prosecutor at the center of the Ukraine controversy said he was told to back off an investigation involving a natural gas firm that was linked to Hunter Biden.

FORMER UKRAINE PRIME MINISTER SAYS COUNTRY MUST INVESTIGATE HUNTER BIDEN

Schweizer said the prosecutor has said under oath in an Austrian court trial that he was "pressured and later fired" because of the Biden investigation, though other Ukrainians have contradicted that claim.

"The bottom line is this needs to be investigated. What we know for a fact is in Ukraine and in China, the only two countries where Joe Biden was point-person on U.S. foreign policy, his son cashed in big time in both countries," he pointed out.

Fox News obtained a copy of Trump attorney Rudy Giuliani’s notes from his January 2019 interview with fired Ukrainian prosecutor Viktor Shokin in which he claimed that his “investigations stopped out of fear of the United States.”

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“Mr. Shokin attempted to continue the investigations, but on or around June or July of 2015, the U.S. Ambassador Geoffrey R. Pyatt told him that the investigation has to be handled with white gloves which, according to Mr. Shokin, that implied 'do nothing,'” the notes from the interview stated.

The notes also claimed Shokin was told Biden had held up U.S. aid to Ukraine over the investigation. Shokin was fired in April 2016, and his case was “closed by the current Prosecutor General Yuriy Lutsenko,” according to the notes.

Despite his claims, Shokin, on both sides of the Atlantic, had been widely accused of corruption.

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Schweizer said it was "ridiculous" for Biden to claim recently to Fox News correspondent Peter Doocy that he had never spoken to his son about his overseas business dealings. A photo obtained by "Tucker Carlson Tonight" showed Biden and his son Hunter golfing in the Hamptons with Devon Archer, who served on the board of the Ukrainian natural gas company Burisma Holdings with Hunter.

"It's a patently ridiculous position, and I think it's one of the reasons the Senate needs to look at this and we need to look at financial records and see the communications that Joe Biden had with Ukrainian and Chinese officials," he said.

Fox News' Brooke Singman contributed to this report.