Sosthène Munyemana was born in 1955 in Gitarama, in Rwanda. He was an obstetrician and gynaecologist in Tumba.
On 7 April 1994, when the massacres began, thousands of Tutsi refugees fled to Butare, which was traditionally known for its peaceful coexistence between the different communities of the country.
On 17 April 1994 in a public speech, Munyemana allegedly incited Hutus to exterminate the Tutsi community of Tumba.
This speech is alleged to have encouraged the inhabitants of Tumba, especially Hutus, to locate Tutsis in the city.
On 21 April 1994, the outbreak of systematic massacres occurred in the area of Tumba. The first victims were intellectuals and Tutsi businessmen. He is reported to have distributed ammunition and compiled lists of Tutsis to eliminate. Munyemana also 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 a list of families to attack during nights.
Moreover, between April and June 1994, Munyemana reportedly went regularly to his home commune of Rusambira to ensure that the Tutsi extermination campaign was going well.
At the end of June 1994, Munyemana fled Rwanda. In October 1994, he and his wife were employed by the University of Bordeaux, where he coordinated a working group on AIDS in Rwanda.