Evidence presented Thursday against Dominic Ongwen, described as the "tip of the spear" of the Lord's Resistance Army, shed light on the ruthlessness of a group that took up arms against the Ugandan government in the 1980s.
Ongwen, who for years was an LRA commander, faces 70 charges involving war crimes and crimes against humanity.
Prosecutor Benjamin Gumpert told the court that witnesses will testify that Ongwen "instructed his personal escorts to administer dreadful beatings," forced prisoners to slaughter innocent people and, on at least one occasion, "to kill, cook and eat civilians who had been abducted in attacks."
The proceedings are intended to confirm the charges against Ongwen before the international tribunal, where judges will determine whether there is sufficient evidence for him to stand trial.
Ongwen, who was born in 1975 in Uganda, was one of the highest-ranking commanders of the LRA, which initially operated in Uganda but later spread to the Democratic Republic of Congo, the Central African Republic and the territory of what would become South Sudan.
In radio communication intercepted by the Ugandan Army, Kony is heard praising Ongwen's tactics as an example for other commanders to follow, according to prosecutors.
Kony is wanted by the International Criminal Court for alleged war crimes. He is accused of recruiting underage boys as fighters and girls as sex slaves, and is the subject of a massive manhunt aided by U.S special forces.
Prosecutors allege that between June 2003 and October 2004, Ongwen was directly involved in attacks on four camps for internally displaced people in which scores of civilians were killed.
"This was not just a civil war between people of uniforms" but "indiscriminate acts of murder" against civilians, Gumpert said, as he showed the court images of burned huts and the bodies of children in one camp.
Ongwen is also accused of operations involving the abduction of children to be soldiers and sex slaves, according to prosecutors.
A UNICEF study estimates at least 66,000 children and young people were abducted by the LRA between 1986 and 2005. Nearly 2 million people were displaced by the violence during conflict.
Ongwen himself was a victim at one time, according to prosecutors. A former commander of LRA's Sinia Brigade, Ongwen told the court he was abducted from his home by an earlier generation of LRA fighters when he was 14.
"We recognize that there may be thought to be something of a paradox in the fact that the stories told by so many of the witnesses in this case could in other circumstances be the story of Dominic Ongwen himself," Gumpert said. "But this is no reason to expect that crimes can be committed with impunity. We have a choice as to how we behave, and when that choice is to kill, to rape and to enslave, we must expect to be held to account."
Ongwen surrendered to authorities in January 2015. He was later transferred to the international court's detention center.
The U.S. State Department is offering $5 million for information leading to the "arrest, transfer or conviction" of Kony and other top leaders of his group.