Abstract
Specialist in the contemporary history of Rwanda, Florent Piton explains the heuristic interest of the hypothesis of precedent in the study of mass crimes, beyond the essential methodological caution. As a practitioner of a study of the history of mass violence over time, he pleads not to neglect, and on the contrary to invest completely, the part of the antecedents in the genesis of these crimes, as in Rwanda for the genocide of Tutsi of 1994, preceded by several episodes of significant collective violence such as the massacres of 1962-1963 or the "Rwandan All Saints Day" of 1959.