Tunisian authorities are trying former President Zine el Abidine Ben Ali in absentia Tuesday for his alleged role in the death of protesters in January 2011.
Ben Ali was ousted in the first uprising of last year's Arab Spring and fled the country. A military tribunal is hearing the case of the former president and dozens of former senior officials.
The trial focuses on who gave orders for snipers to shoot 41 protesters, an emotionally charged question in the north African country.
Nearly 250 people died over the course of several weeks early last year before Ben Ali fled to Saudi Arabia.
Among the most prominent defendants to appear Monday was the former director general of public security, Lotfi Zwawi, who repeatedly said he "knew nothing, saw nothing, and heard nothing of civilian casualties."
The former president has already been tried and convicted in absentia for his role in a 1991 case in which 17 servicemen were accused of plotting a coup against his regime, the agency Tunis Afrique Presse said in November.
A Tunisian military court sentenced him to five years in prison, the state-run Tunisian News Agency said November 30.
The defense plans to appeal, it added.
Egypt's former president, Hosni Mubarak, is on trial in his own country over the killing of protesters during the uprising that forced him from power weeks after Ben Ali fled Tunisia.