Joseph Smith's Last Letter
The very last letter he penned from the jail, mere hours before he was killed, wasn't to his wife, another Church leader, or a governmental officer (though he wrote letters to all of them earlier that day): it was to his big-city lawyer, imploring him to hurry up and arrive before the scheduled trial so they could prepare. The lawyer got the letter and started off for Carthage but when he arrived his client was dead. Instead of wasting a trip, he stuck around and was soon hired to represent the few members of the mob eventually called to trial for the murder, and he was successful in getting them all acquitted. I guess Joseph was just being nice and wanted his killers to not experience any justice for his death because he was just a nice guy like that.
June 27, 1844
Joseph Smith dictated a letter from Carthage Jail to his wife Emma. In his own hand he penned a postscript that included the following: "I am very much resigned to my lot knowing I am Justified and have done the best that could be done give my love to the children and all my Friends." Joseph then dictated a letter to lawyer Orville H. Browning, requesting his professional services.
Personal Writings of Joseph Smith, Joseph Smith, pp. 629–35
Time line listing it last: https:⁄⁄jschronology.byustudies.byu.edu⁄events⁄june-27-1844
The letter itself: https:⁄⁄www.josephsmithpapers.org⁄paper-summary⁄letter-to-orville-browning-27-june-1844⁄1
For Browning's defense of the Carthage conspirators: Oaks, Dallin H.; Hill, Marvin S. (1979). Carthage Conspiracy: The Trial of the Accused Assassins of Joseph Smith. Champaign, IL: University of Illinois Press, pp. 79-83.
History of the Church, Vol 6, Chapter 34 (pp. 613-614) (I know, I know, it's a terrible historical source, but this is technically part of the story that hasn't been actively hidden but amazingly no TBM seems to want to dwell on it) talks about how this letter to Joseph's lawyer becomes the very pretense needed for the mob to assemble:
Almon W. Babbitt took the letter and left the jail. He handed it to Jones, with directions to take it to Quincy forthwith. The guard being aware of the letter, told the mob that, "old Joe" had sent orders to raise the Nauvoo Legion to come and rescue him. The mob gathered around Jones, and demanded the letter; some of them wanted to take it from him by force, and said that Jones should not get out of Carthage alive, as a dozen men had started off with their rifles to waylay him in the woods. Having previously ordered his horse, Jones took advantage of their disagreement, and started off at full speed. He, by mistake, took the Warsaw road, and so avoided the men who were lying in wait for him. When he emerged on the prairie, he saw the Governor and his posse, whereupon he left the Warsaw road for the Nauvoo road.