An IRS whistleblower who alleged the agency stifled an investigation into Hunter Biden's tax matters is now urging Congress to bring as many witnesses forward as possible to shed light on possible wrongdoing by the first family. 

Gary Shapley, who was the supervisor of the Hunter Biden investigation at the IRS, joined "America's Newsroom" to discuss why Congress needs "additional investigation" into the Biden family's business dealings.

"That was one of the main issues that we brought forward to the House Ways and Means and House Oversight was that we weren't allowed to follow the normal investigative steps that would have potentially shine[d] more light on these issues," Shapley said Tuesday. "We were very specific on what we provided, and those are things that now can be taken, the breadcrumbs that we've left, and they can go and talk to these witnesses, they can go talk to the government, individuals involved, and they can get to the bottom of it because every time that we needed to ask questions about President Biden's involvement and in relation to the business dealings, we just weren't allowed to do that."

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Devon Archer

Devon Archer, a former business associate of Hunter Biden, arrives for closed-door testimony with the House Oversight Committee at the O'Neill House Office Building on July 31, 2023, in Washington, D.C. (Drew Angerer / Getty Images)

"So, there remains a lot of work to be done, and we can't emphasize enough how important it is that they continue to bring in witnesses because each witness that comes in is providing more and more evidence, and it cannot be denied," he continued.

Shapley's remarks come after Hunter Biden's former business associate, Devon Archer, sat down for an hours-long closed-door hearing before the House Oversight Committee on Monday.

Chairman James Comer confirmed that Archer contradicted President Biden's previous claims that he had no knowledge of Hunter's overseas business ventures.

Archer also reportedly said that Hunter put his father, then-Vice President Joe Biden, on speakerphone while meeting with business partners at least 20 times. Archer described how Joe Biden was put on the phone to sell "the brand."

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"We brought a lot of facts and evidence forward to the House Ways and Means Committee and to the House Oversight Committee to include testimony from Rob Walker, WhatsApp messages and … other documents that clearly show that we need to do additional investigation, and Congress needs to go out there," Shapley said. 

But the only Democrat in the closed-door hearing, Rep. Dan Goldman, D-N.Y., downplayed Archer's testimony.

Goldman said his remarks reiterate that the president "had nothing to do with Hunter Biden’s business dealings, derived no benefit from it, received no money and did not know about anything that Hunter Biden was doing, nor did he ever discuss it with Hunter Biden or the business associates."

Despite the discrepancy over the key takeaways of the interview, Shapley doubled down on calls for Congress to speak with as many witnesses as possible as the investigation continues.

"They need to talk to as many people as they can, and that's what we hope they do," he continued. "Devon Archer was just another step in that process to fully investigate the true links to where this ends up to."

"The people of the United States demand that the government get to the bottom of this. They need to talk to all these people. They can’t just allow DOJ to not give access to people."

Shapley previously told Fox News' Bret Baier that the IRS put critical steps in the investigation "on the back burner" ahead of the 2020 presidential election. 

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He also said that "the most substantive felony charges were left off the table," that DOJ prosecutors directed investigators to avoid asking witnesses questions about President Biden, that they chose not to collect search warrants related to the president’s son, and more.

"We weren’t allowed to ask questions about ‘dad,'" he told Baier in June. "We weren’t allowed to ask about ‘the big guy.’ We weren’t allowed to include certain names in document requests and search warrants."

Fox News' Brooke Singman and Elizabeth Elkind contributed to this report.

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