Nyarubuye Cathedral, Rwanda

April 15, 1994, nine days after the start of the Rwanda Genocide, more than 7000 Hutu militia marched down a narrow lane toward the Nyarubuye convent and cathedral — a sacred place known to be a place of refuge for the vulnerable and those in need, which on this day was between 5,000 and 10,000 Tutsi Rwandans.

The mayor, Sylvestre Gacumbitsi, commanded the police to shoot all Tutsi and quickly the local Hutu followed suit — hacking, slashing and bludgeoning their...