Answer:
Joseph Smith and his brother Hyrum were murdered while in custody at the Carthage Jail in Carthage, Illinois. Joseph and Hyrum had been charged with treason for having declared martial law and destroyed a printing press in Nauvoo, Illinois. Joseph was mayor of Nauvoo. He declared martial law and destroyed the press in an attempt to avoid a riot.
The cell in which he was held was on the second floor of the jail. When the mob came up the stairs and attempted to force open the door, they shot and killed Hyrum. Joseph went to the window, looking for an escape. Another mob in the street shot up into the cell and killed him. His body fell out the window to the ground where the mob continued to shoot, stab and kick his dead body.
When someone yelled: "the Mormons are coming!" The mob dispersed, and the other two inmates were spared. The bodies were conducted back to Nauvoo for burial.