Known as the "White Ant", Ongwen faces 70 counts of war crimes and crimes against humanity for his role from 2002 to 2005 in the sinister LRA rebel group, led by its fugitive chief Joseph Kony.
![Austrian Chancellor Karl Nehammer [DW]](data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D'http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg'%20width%3D'100'%20height%3D'100'%20data-ring-placeholder%3D'1'%3E%3C%2Fsvg%3E "Austrian Chancellor Karl Nehammer [DW]")
Ongwen is also the first accused before The Hague-based ICC to face the very same charges of which he is also a victim.
Born in 1975, Ongwen was abducted as a young boy while walking to school and was soon trained as a child soldier within the LRA.
Prosecutors said he grew up to become a "ferocious" senior LRA commander in charge of Kony's infamous Sinai brigade -- which among many crimes committed also abducted young girls and women to serve as domestic workers and sex slaves.
Ongwen was "enthusiastic in adopting the LRA's violent methods and eager to show he could be more active and more brutal" than others, prosecutors said as his trial opened in January 2016.
ICC chief prosecutor Fatou Bensouda at the time played a gruesome video depicting the aftermath of an LRA attack on a refugee camp, shocking the courtroom with images of disemboweled children and charred bodies of babies in shallow graves.
In another attack against the Odek refugee camp in 2004, Ongwen instructed his troops that "nothing should be left alive," prosecutors said.
A victim too?
Ongwen, now around 43, has denied the charges, insisting it was the LRA, not him, who murdered defenceless refugees.
"Mr Ongwen has been clear from the beginning... that the charges before the court are not against him, but rather against the LRA, and that the LRA is not his army," his lawyer Krispus Ayena Odongo said.
"He was just a victim, like many others (who were) abducted like him," Odongo told AFP ahead of the opening of the defence's case.
Physically "Dominic Ongwen was doing fine" Odongo said. His client however has been diagnosed with severe post-traumatic stress disorder.
Ongwen's case before the ICC is unique, said international law expert Mark Kersten of the University of Toronto.
"The trial throws up so many important questions as to how to deal with victim-perpetrators," he told AFP, including the appropriate type of punishment should Ongwen be found guilty.
Bloodthirsty rebels
A self-styled mystic and prophet, Kony launched a bloody rebellion more than three decades ago seeking to impose his own version of the Ten Commandments in northern Uganda.
The UN says the LRA has slaughtered more than 100,000 people and abducted 60,000 children since it was set up in the mid-1980s.
More than 4,000 victims are also taking part in Ongwen's trial which began more than a decade after a warrant for his arrest was issued in 2005.
Ongwen was transferred to the ICC in 2015 shortly after surrendering to US special forces operating in the Central African Republic.
At the time, former US president Barack Obama had deployed a small number of US troops to the region to aid the hunt for Kony, who is still at large.
Experts believe Ongwen fled after falling out with Kony and almost being killed.
The LRA first emerged in northern Uganda around 1986, where it claimed to fight in the name of the Acholi ethnic group against long-time President Yoweri Museveni's government.
Over the years, the LRA has moved across porous regional borders: it has shifted from Uganda to sow terror in southern Sudan before moving into northeastern Democratic Republic of Congo, and finally crossing into the Central African Republic in 2008.
Combining religious mysticism with an astute guerilla mind and bloodthirsty ruthlessness, Kony remains a fugitive and nothing is known of his current whereabouts.
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