Looking tired and pausing several times to drink water, Aziz - once the public face of Saddam's regime - blamed Iran for a gas attack in the Iraqi Kurdish village of Halabja in 1988, in which 5,000 people were killed.
"The chemical weapons used at that time causing the death of thousands of people were made with cyanide gas and not mustard gas. Iran had this gas at this time, not Iraq," said Aziz.
Aziz said that two papers he obtained on the Internet while he was in office prove his claim. He said one was a report from an "Institute affiliated to US department of defence called 'Seaman' which was published in 1989".
He said the other was an article written by Milton Viorst for the New Yorker magazine.
Aziz went on to say that meetings between the former Iraqi leadership and a Kurdish delegation that included the present Iraqi president Jalal Talabani took place in 1991.
According to Aziz, "the talks focused on the compensation of Kurdish war victims" and that the Halabja tragedy was not mentioned by either party.
Halabja is not part of the Anfal case, but prosecutors hope to open soon a separate trial on Halabja.
Aziz, who was once known for his love of fine suits, good whisky and Cuban cigars, also testified as a defence witness in the Dujail case, for which Saddam was hanged in December.
His lawyers have said he is suffering from diabetes and other illnesses.
Aziz has not been charged with any crime but prosecutors at the Iraqi high tribunal have said he will likely face charges for his role in crushing a Shia uprising after the 1991 Gulf war.