The most immediate Protestant target of the St. Bartholomew's Day massacre in 1572 was Admiral Gaspard de Coligny, despised by key elements of the Catholic leadership for personal as well as sectarian reasons dating back a decade to the origins of the Wars of Religion. 
Historian Barbara Diefendorf pieces together the situation in Paris on the eve of the St. Bartholomew's Day massacre: a Catholic population primed with an essentially genocidal fury at the presence of Protestants, awaiting the slightest signal to act: jstor.org/stable/1859659
One thing Diefendorf draws attention to is the fact that the Protestants murdered during the St. Bartholomew's Day massacre by the Catholic mobs were not random; starting with Coligny, these were targeted assassinations based on resentments from ten years of religious war:
Papal Medal struck by Pope Gregory XIII, "Ugonottorum Strages (Slaughter of the Huguenots), 1572", celebrates the extermination of a large proportion of the Protestants of France in the St. Bartholomew's Day Massacre, a victory he considered on the level of Lepanto.
