“His guilt has been established beyond any reasonable doubt,” presiding judge Bertram Schmitt said as he read out the verdict in the tribunal in The Hague.
Ongwen, nicknamed “White Ant”, was convicted of charges including murder, rape, sexual enslavement and the conscription of child soldiers. He had denied all the charges.
Judges rejected defence arguments that Ongwen was himself a victim, as he had been abducted by the LRA at the age of around nine and suffered psychological damage as a result.
“The chamber is aware that he suffered much,” judge Schmitt said. “However this case is about crimes committed by Dominic Ongwen as a responsible adult and a commander of the Lord’s Resistance Army.
“The chamber did not find evidence for the claim by the defence that he suffered from any mental disease or that he committed the crimes under duress,” Schmitt said.
‘Shot, burned and beaten’
Human Rights Watch said the case was a landmark in achieving justice for victims of the Lord’s Resistance Army.
“This case is a milestone as the first and only LRA case to reach a verdict anywhere in the world,” Elise Keppler, associate director of the International Justice Program at HRW, told AFP.
The LRA was founded three decades ago by former Catholic altar boy and self-styled prophet Kony, who launched a bloody rebellion in northern Uganda against President Yoweri Museveni.
The United Nations says the LRA killed more than 100,000 people and abducted 60,000 children in a campaign of violence that spread to three other African nations — Sudan, the Democratic Republic of Congo and the Central African Republic.
Judges said Ongwen — whose nom de guerre means “born at the time of the white ant” — ordered his soldiers to carry out massacres of civilians at the Lukodi, Pajule, Odek, and Abok refugee camps.
Children and mothers with babies tied to their backs were among those killed, said judge Schmitt, who read out the names of the victims.
“Civilians were shot, burned and beaten to death. Children were thrown into burning houses, some were put in a polythene bag and beaten to death,” Schmitt said.
Dumped in a rubbish pit
Ongwen, as commander of Kony’s infamous Sinia brigade, was responsible for the abduction of girls to serve as domestic workers and sex slaves, and boys to serve as soldiers, judges said.
During 2002-2005, seven of these women were forced to be Ongwen’s “so-called wives” and two gave birth to children, leading to the historic conviction for forced pregnancy.
Soldiers under Ongwen’s command forced some mothers abducted by the group to abandon their crying babies in the bush so they could carry supplies. One two-month-old was dumped in a rubbish pit.
At the opening of the trial, prosecutors played gruesome videos of the scene after an LRA attack on Lukodi refugee camp, showing disemboweled children and the charred bodies of babies in shallow graves.
Kony promoted Ongwen to colonel at about the time of the attack, the judge said.
Residents in Lukodi near the city of Gulu, some 350 kilometres (220 miles) north of Kampala, told AFP the horrors of the attack still lingered fresh in their memories.
“A total of 15 of my family members were killed during the attack and very many people were injured,” said farmer Muhammed Olanya, 38.
Ongwen surrendered to US special forces who were hunting Kony in the Central African Republic in early 2015 and was transferred to the ICC to face trial.