Guinea opened a landmark trial Wednesday 13 years after a stadium massacre by the military left at least 157 protesters dead and dozens of women raped, with the country’s former coup leader Moussa “Dadis” Camara among those charged.

The court proceeding began a day after Camara and five more defendants were detained in the capital, Conakry, pending the outcome of the trial. A dozen men in total have been charged with crimes including murder and rape in connection with the 2009 attacks.

“Thirteen years later, let’s do everything possible to ensure that the horror of massacres does not happen again in Guinea,” said Djibril Kouyate, the president of the Guinean National Bar Association, during a speech at the trial’s opening. “Those who died will not speak again, but their bloodshed demands justice.”

Karim Ahmad Saad Khan, the chief prosecutor of the International Criminal Court, told those gathered Wednesday that “13 years is a long time” and applauded the victims’ family members for keeping their patience.

“September 28 has become a day of sadness,” he said. “We have the opportunity, you have created the space for September 28 to be a day of promise and hope.”

Demonstrators had gathered at the stadium that day to protest then-coup leader Camara’s plans to run for president when security forces opened fire. The junta said that “uncontrolled” elements of the army carried out the rapes and killings. But a Human Rights Watch investigation found that Camara’s top aides were at the stadium and did nothing to stop the violence.