Bradley Birkenfeld on Wednesday disowned records indicating that he had signed some of the security supplies contracts.
The FBI agent had been requested by the Kenyan government to assist in the investigations.
On Wednesday, Mr Tariche said he was not aware of the Kenyan arrest warrant against Mr Birkenfeld.
Questions emerged on Wednesday over the integrity of an American witness in the Anglo Leasing suit after he disowned, through an FBI agent, statements tabled in court by the Ethics and Anti-Corruption Commission (EACC).
Bradley Birkenfeld on Wednesday disowned records indicating that he had signed some of the security supplies contracts.
The EACC on April 21, 2015 disclosed to the court that Mr Birkenfeld, 50, signed crucial documents as the managing director of Infotalent—one of the firms that supplied security items under the Anglo Leasing contracts.
The EACC has said in court papers that Mr Birkenfeld signed a supplier’s finance agreement and documents for direct procurement as Infotalent’s managing director.
Wednesday, Mario Garcia Tariche, the special Agent with the FBI told the anti-corruption court that Mr Birkenfeld had indicated that the signatures were not his.
The FBI agent had been requested by the Kenyan government to assist in the investigations.
“Mr Birkenfeld said he did not sign the contract and the address indicated was his home address and not office address,” said Mr Tariche in reference to the interview he conducted on June 11, 2015.
But Mr Tariche was at pains to explain why an affidavit referring to the June 11, 2015 meeting indicates he signed it on June 6, 2015, days before the said meeting actually took place.
Mr Birkenfeld, who was initially a suspect in the Anglo Leasing suit, has declined to testify personally in Kenya citing security fears.
The court had issued a warrant of arrest against Mr Birkenfeld when he was being interviewed by the FBI agent.
In the US, the American was a prosecution witness who helped expose widespread tax fraud by wealthy Americans using Swiss bank accounts.
A former employee at Swiss bank UBS, he also served two years in jail for helping a rich American in California dodge federal taxes.
On Wednesday, Mr Tariche said he was not aware of the Kenyan arrest warrant against Mr Birkenfeld.
Lawyer Ahmednasir Abdullahi for defence said that Mr Birkenfeld was converted to a witness by the prosecution following an agreement that he implicates other people in exchange for his freedom.
In the suit, former senior government officials and businessmen have been charged in connection with multibillion-shilling security tenders in 2003 that the government cancelled as irregular. Hearing resumes on November 20.
