"Some were shot dead in their sleep, some cut up by machetes to save bullets. Others were burned alive after their houses were set on fire by the attackers," Chief Prosecutor Luis Moreno-Ocampo said, adding others were shot as they fled.
Katanga, 31, an ethnic Ngiti, is said to have commanded the Patriotic Resistance Force (FRPI). Ngudjolo, 39, a Lendu, is accused of being the former leader of the National Integrationist Front (FNI).
Both men are charged with seven counts of war crimes and three charges of crimes against humanity, including murder, sexual slavery, rape, using child soldiers, pillaging and destruction of property.
After the trial started, both men were asked if they understood the charges and to enter pleas to all 10 counts.
"I have said since I arrived here that I am not guilty. I still continue to plead not guilty," Katanga said, speaking through an interpreter, and in response to each subsequent charge added: "I plead not guilty."
Ngudjolo gave a similar response to each charge: "Your honor, I plead not guilty."
Moreno-Ocampo said both the FRPI and FNI were in conflict with the Union of Congolese Patriots (UPC), mostly of Hema ethnicity, and attacked the village of Bogoro to open up a road link and prevent UPC attacks against Ngiti and Lendu targets.
He said hundreds of women, men and children under the command of Katanga and Ngudjolo attacked the village in successive waves of violence at 5.30 in the morning, using automatic weapons, machetes and spears.
Moreno-Ocampo said the militias did not distinguish between military and non-military targets and villagers who tried to find refuge at a UPC camp in the village were "easy prey." Bodies of dead civilians filled the rooms of the UPC camp building.
The defense is due to give its opening statements later on Tuesday along with two legal representatives of more than 340 court-recognized victims, 10 of whom are child soldiers.
Prosecutors will call 26 witnesses, 21 of whom are protected witnesses. The trial is expected to take several months.


