On September 11, 1857, the Mountain Meadows Massacre tookplace. Mormons dressed as Indians murdered 120 colonists in Utah. From the article:
"On Friday, September 11, hope appeared in the form of a white flag. The emigrants let the emissary, a Mormon from a nearby settlement, into their fort, and then John D. Lee, the local Indian agent, followed. Lee told the Arkansans he and his men had come to rescue them from the Indians. If the emigrants would lay down their arms, the local militia would escort them to safety. The travelers had few options: they surrendered and agreed to Lee’s strange terms."