On September 7, 1857, Mormon militia and Paiute allies attacked a wagon train of Arkansas emigrants in southern Utah, beginning a five-day siege that ended with the killing of roughly 120 unarmed men, women, and older children. The men who planned it saw themselves as a persecuted people defending against invasion, not as murderers, and the cover-up that followed lasted a century and a half before the church responsible fully acknowledged its role. This episode traces how religious certainty, war hysteria, and institutional self-protection combined to produce one of the darkest chapters of American westward migration, and how long the truth took to surface.