Larochelle told Hirondelle News Agency that his client pleaded not guilty to the charges on crimes allegedly committed in Kibuye prefecture, Western Rwanda.
He is accused of participating in massacres of Tutsis in two churches and one hospital in the prefecture.
According to Canadian Press (CP), Marc Lishchynski, the lead Royal Canadian Mounted Police (RCMP) investigator, became the first to enter the witness box for the prosecution.
He is quoted as telling the court that he visited Rwanda "100 times" and presented detailed photos and satellite pictures of where some of the atrocities occurred.
The taking off of the trial for the Rwandan teacher comes after the International Criminal Tribunal for Rwanda (ICTR) rejected his requests, seeking right to use materials of several witnesses who had testified in different cases before the Tribunal.
Born in 1972 in Rwanda, Mungwarere was a teacher in Kibuye. He arrived in Canada in 1998 and obtained refugee status in 2002. He worked as temporary warehouseman in a factory of Windsor, South of the Ontario in Canada, where he lived with his wife and his three children.
The Royal Canadian Mounted Police (RCMP), in Windsor, arrested Mungwarere on November 6, 2009, in cooperation with Rwanda's Genocide Fugitive Tracking Unit (GFTU).
He is the second Rwandan to be prosecuted under Canada's crimes against humanity and war crimes Act, which was introduced in 2000, allowing for prosecution no matter where or when an alleged war crime may have been committed.
The first Rwandan to be tried under the crimes against humanity and war crimes law in Canada was Desire Munyaneza, who was convicted in 2009 and sentenced to life in prison.