On Monday, Ghannouchi appeared before a tribunal as a witness in the trial probing manslaughter charges against Ben Ali and his key aides, held in Le Kef, some 170 kilometers northwest of the capital Tunis.
The military tribunal is investigating the killings of protestors in the central-western towns of Thala and Kasserine where 22 protesters were murdered by government forces during the country's revolution early last year.
Ben Ali's regime collapsed on January 14, 2011 after weeks of bloody protests over corruption, unemployment, and high food prices. He fled to Saudi Arabia with his family on the same day.
The popular revolution sparked a wave of anti-regime protests in North Africa and Middle East, promptly known as the Islamic Awakening, and led to the downfall of long-time dictators in Egypt and Libya.
The tribunal is trying Ben Ali in absentia with 23 others, including two of his former interior ministers, and several top security officials, who are accused of being responsible for the killings of protesters and injuring hundreds in the two towns.
Ghannouchi, who led the first transition government until February 27, 2011, testified that Ben Ali wanted to "kill a thousand or more" people demanding an end to his 23-year dictatorship.
He said he called Ben Ali on January 9, 2011 and requested him to stop his security forces for using live bullets on protestors in Kasserine but the former ruler justified it as a legitimate defense given the attacks on police posts.
“This was Ben Ali's response to my request to stop firing live rounds," Ghannouchi said.