This is what Judge Michel Charbonneau must decide in Canada's second trial under the Crimes Against Humanity and War Crimes Act.
On Monday, Mungwarere pleaded not guilty to one count of genocide by murder, and one count of crimes against humanity by murder, as his trial began in Ontario Superior Court. He had already opted against a jury trial.
The bright-eyed, young-looking, 40-year-old arrived at court wearing a white dress shirt, a black vest and pants. He was arrested in 2009 in Windsor, Ont., following an RCMP investigation that began in 2003. Mungwarere arrived in Canada roughly three years earlier as a refugee, and has a wife and two children.
The trial is likely to last months, as details of the investigation are laid before the court, and witnesses from different locations appear both in person and by video-link.
Marc Lishchynski, the lead RCMP investigator, told court he visited Rwanda 100 times. The court saw detailed photos and satellite pictures of where some of the atrocities occurred.
The horrific days of 1994, when 800,000 Rwandans of mostly Tutsi descent were massacred by the Hutu majority, were described in some detail in the sedate courtroom Monday.
Mungwarere is accused of participating in a massacre of Tutsis in the region of Kibuye. Thousands of people had sought refuge in a local hospital, believing they might find sanctuary.
Prosecutor Luc Boucher said local militias encircled the low brick compound on April 16, 1994, and began shooting and slaughtering the people inside. Mungwarere is accused of shooting some of the victims himself.
Some escaped the hospital and ran to the outlying hills. Mungwarere is alleged to have helped hunt down and kill fugitives.
Boucher said one witness who was forced to abandon a baby so he could survive on foot will testify that Mungwarere subsequently shot the child in the head. Other witnesses are expected to testify that they saw Mungwarere regularly meet members of the militia group that was hunting down Tutsis.
"The witnesses will come in the coming weeks to testify to the effect that ... he participated in attacks that were planned and caused the deaths of a lot of people, and the plan was the extermination of the Tutsi ethnic group," Boucher said outside court.
"There was no discerning between children, women, men during the massacres. They did not distinguish."
Mungwarere's defence team, lead by Marc Nerenberg, is set to argue that the testimony of the witnesses is a complete fabrication based on their own various agendas.
He said Mungwarere was fingered as a potential murderer three weeks after he agreed to testify for the defence at the trial of another Rwandan in the United States.
"The basis of the defence is that the accusations are fabricated, that the witnesses who are testifying against him made it up. It didn't happen," said Nerenberg.
"He was there and he did not participate in the genocide in any way."
Nerenberg said his client had lobbied successfully for more leeway in prison to help put together documentation that will help prove his innocence.
The Crown's first witness was Rwanda expert and author Timothy Longman, who spent years in the lush African country both immediately before and after the genocide.
Longman, a political science professor at Vassar College, described in detail how tensions built up in Rwanda over the last century, fuelled by a largely artificial division of the population along ethnic lines that was perpetuated by the German and Belgian colonial regimes.
He also made clear that he has serious difficulties with the current regime in Rwanda, which he described as a dictatorship that has tried to quash dissent and silence critics.
Nerenberg focused on this element in his cross-examination of Longman, underlining the weaknesses of the genocide-tribunal system in Rwanda that put justice in the hands of citizens at the community level rather than judges and lawyers.
Roughly 250,000 individuals had been elected to the local tribunals, only receiving a week of training as they helped prosecute roughly 900,000 accused.
Longman acknowledged that there had been cases of false accusations, sometimes based on competing interests such as claims on land.
"Isn't it so, that Tutsis who make false accusations have basically nothing much to fear?" Nerenberg asked Longman.
Longman said there has been a policy of reduced sentences for those who confess to their crimes and they must also present evidence against others. He said that has resulted in some Hutus accusing others of atrocities, often people already in jail.
And Longman said the government has tried to quash its critics by accusing them of being pro-genocide.
The first person to be tried under the Crimes Against Humanity and War Crimes Act, Rwandan Desire Munyaneza, was convicted in 2009 and sentenced to life in prison without a chance of parole for 25 years.