The trial, hailed as a breakthrough by the United Nations, opened more than four years ago, with Ignace Murwanashyaka, head of the Democratic Forces for the Liberation of Rwanda (FDLR) and his deputy Straton Musoni charged over a litany of war crimes.
The two Rwandans, who have lived in Germany for more than 20 years, were accused of "the full range of atrocities that one can imagine in a civil war", said federal prosecutor Christian Ritscher.
At the opening of the case, Ritscher said Murwanashyaka ordered more than 200 killings and "large numbers" of rapes by his militias, had them use civilians as human shields and sent child soldiers into battle in eastern Congo.
The two men were initially accused of 26 counts of crimes against humanity and 39 counts of war crimes committed by militias under their command between January 2008 and their arrest in Germany in November 2009.
But over time, that was whittled down to charges related specifically to the killings, as the court decided not to further aggravate the vulnerability of traumatised rape victims or child soldiers by making them appear before the hearing.
Nevertheless, the case was welcomed as groundbreaking by the UN, after repeated calls by the Security Council to bring FDLR commanders living abroad to justice.
It was also closely followed by human rights groups which believe that it "serves as a warning against all those individuals suspected of having committed war crimes".
"The justice system could have stopped at the terrorism charge. To prosecute crimes against humanity, despite the problems linked to proving the claims, sends a strong signal," said Andrej Umansky, criminal law expert at Cologne University.
FDLR still sowing terror
The defence has contested the alleged chain of command at the FDLR, arguing that the accused are simply political leaders who have no say over the atrocities being committed in Congo.
"What's the difference between Musoni and Alan Doss?" asked Musoni's lawyer Jochen Theilmann, making a reference to the then chief of the UN mission in Congo (MONUSCO).
MONUSCO had backed the Congolese army's offensive against the FDLR, which had in turn also been plagued by massacres.
The defence is seeking a full acquittal.
But prosecutors are pushing for life imprisonment for Murwanashyaka with no conditional release after 15 years as is usual practice under Germany's legal system. They are seeking 12 years for Musoni.
The FDLR was formed in 1994 by ethnic Hutus, including perpetrators of the Rwandan genocide, who fled to neighbouring Congo after President Paul Kagame took power.
It is today still sowing terror in resource-rich Congo, despite repeated efforts by UN troops and Congolese forces to stamp out the violence.
But beyond this case, legal experts believe the verdict could be a trailblazer for other serious crimes committed abroad to be tried in Germany.
According to Kai Ambos, international criminal law professor at Goettingen University quoted by DPA news agency, the German justice system has seen an increasing number of claims filed by Syrians over crimes perpetrated in the
war-torn country by both regime forces and militants from the Islamic State (IS) group.
"If German fighters from Daesh (IS) return to Germany, some of them could face charges, given that the International Court of Justice does not have jurisdiction to deal with such complaints as Iraq and Syria have not signed the convention," Umansky said.
But he raised the question of whether these fighters would be charged with crimes against humanity, or whether Berlin would just seek terrorist charges.
"The easier route appears to be terrorism, which is also politically less delicate," he said.