On June 27, 1844, Joseph and Hyrum Smith were killed by a mob that stormed the Carthage Jail. BYU Studies has published several articles and documents that record the martyrdom and tell of its effect on the Saints. Here are some key publications:
"John Taylor's June 27, 1854, Account of the Martyrdom," LaJean P. Carruth and Mark L. Staker
On June 27, 1854, Elder John Taylor gave what appears to be his first public address sharing his eyewitness account of the martyrdom of Joseph and Hyrum Smith. This shorthand account is incomplete and thus is supplemented with a later copy of the same public address. Taylor gives his testimony of Joseph as a prophet, the legal circumstances of the arrest and detainment at the jail, and the events of the assault at the jail.
"Road to Martyrdom: Joseph Smith's Last Legal Cases," Joseph I. Bentley
This article tells of the actions of six men (Francis and Chauncey Higbee, William and Wilson Law, and Robert and Charles Foster) who were key actors in the events leading up to the martyrdom. It examines the legality of the destruction of the Expositor and the charge of treason against Joseph and Hyrum Smith.
"Life in Nauvoo, June 1844: Vilate Kimball's Martyrdom Letters," Ronald K. Esplin
Vilate Kimball's letters provide a detailed view of the emotional and confused atmosphere in Nauvoo during the two weeks leading up to the murders, as well as give an insight into the impact on the city of the event itself. Heber C. Kimball's journal tell how much Vilate's letters meant to him. In 1844, after concluding to become a candidate for President of the United States, Joseph Smith sent out from Nauvoo hundreds of preaching and electioneering missionaries. These included some of the Twelve, who were also to seek Congressional redress for past wrongs to the Mormons.