An arsonist set fire to the Temple. The Keoukuk Register reported that "Great volumes of smoke and flames burst from the windows, and the crash of falling timbers was distinctly heard on the opposite side of the [Mississippi] river. The interior of the building was like a furnace, the walls of solid masonry were heated throughout and cracked by the intense heat. The melted zinc and lead were dropping from its high block during the day." ...
Brigham Young later said of the arson, "I hoped to see it burned before I left, but I did not. I was glad when I heard of its being destroyed by fire, and of the walls having fallen in, and said, 'Hell, you cannot now occupy it.'"
[The ruins would be leveled by a tornado in 1850.]
[Brown, Lisle (compiler), Chronology of the Construction, Destruction and Reconstruction of the Nauvoo Temple]