Ziegler had remained anonymous until his appearance at a House oversight committee hearing on Wednesday that was convened over Republican allegations that President Joe Biden and his son Hunter were involved in a bribery scheme with Burisma.
When asked by panel chairman James Comer, Ziegler, referencing a binder with bank statements, confirmed "Burisma paid to everyone involved 6.5 million [dollars]."
In the same exchange with Comer, the IRS agent also confirmed payments made to Blue Star Strategies, a consultancy that worked with Burisma when Hunter Biden was on its board, and other law firms involved.
"Burisma also paid Blue Star strategies and a law firm hundreds of hundreds of thousands of dollars bringing the total Burisma payments to over $7 million. Is that correct?" Comer asked, to which Ziegler responded with: "That is correct. 7.3 million."
The total amount of money Hunter and his business associates received from foreign sources amounted to $17 million, according to Ziegler.
"It appeared to me based on what I experienced that the US Attorney in Delaware in our investigation was constantly hamstrung, limited and marginalized by DOJ [Department of Justice] officials, as well as other US attorneys," Ziegler said in congressional testimony on Wednesday.
"Assigned prosecutors did not appear to follow the normal investigative process, slow-walked the investigation, and put in place unnecessary approvals and roadblocks from effectively and efficiently investigating the case."
The IRS agent also said they uncovered evidence that supported felony tax evasion charges, although US authorities indicted Hunter Biden on misdemeanor tax charges, in addition to a felony gun charge.
The whistleblower in his closing remarks also advised that a special counsel be appointed to pursue the Biden case even further.
Hunter Biden’s attorneys and the US Justice Department announced last month an agreement under which he will plead guilty to misdemeanor tax charges and enter a pretrial diversionary agreement on a felony firearms offense in an effort to resolve the criminal probe against him and avoid prison time.