Sosthène Munyemana was born on 1955 in Gitarama, in Rwanda. He is an obstetrician gynecologist in Tumba.
On 7 April 1994, when massacres began, thousands of Tutsi refugees fled to Butare, traditionally known for its peaceful coexistence between the different communities of the country. Thousands of them were murdered there.
On 17 April 1994, Munyemana was appointed security officer for some streets of Tumba. He allegedly made a speech in which he clearly expressed his intention to exterminate the Tutsi community of Tumba. His speech is alleged to have encouraged the inhabitants of Tumba, and in particular Hutus, to locate Tutsis in the city. This speech has reportedly contributed to a large extent to the outbreak of the genocide in Tumba.
On 21 April 1994, the outbreak of systematic massacres occurred in the area of Tumba. The first victims were intellectuals and Tutsi businessmen.
Munyemana allegedly participated directly in the attacks, but he also reportedly commanded a group of soldiers. Appointed team leader of the night watch, Munyemana allegedly made lists of families to attack at night.
Moreover, between April and June 1994, Munyemana reportedly went regularly to his home commune of Rusambira to ensure the Tutsi extermination campaign was going well.
At the end of June 1994, Munyemana fled Rwanda. In October 1994, he and his wife were recruited by the University of Bordeaux, where he coordinated a working group on AIDS in Rwanda.