A confession etched on a newly discovered lead sheet has shaken the Mormon Church by linking its revered leader, Brigham Young, with one of the worst massacres in US history.
The note claims that the founder of Salt Lake City ordered the 1857 Mountain Meadows Massacre, when a wagon train of 120 settlers, mostly women and children, were killed after having thrown down their weapons on a promise of safe passage.
The Church of the Latter-Day Saints, as Mormons are known, tried to blame Indians for the slaughter, but - after pressure from the Federal Government - John Lee, a militiaman who was Mr Young's adopted son, was executed for organising the attack.
The church has always maintained the militia acted alone, despite claims that documents incriminating church leaders were burnt at the end of the 19th century. Schoolbooks in Utah do not mention the massacre, and it has been airbrushed out of the religion's official history.
The lead sheet was found during restoration work on the debris of the citadel at which Lee's militia forces were based on the Colorado River, under soil and rat droppings.
It is signed by Lee, who had 19 wives and 64 children, and claims to be written "by my own hand", 15 years after the events it describes. Filled with grammatical errors, it says: "I do not fear athorty for the time is closing and am willing to take the blame for Fancher."
The wagon convoy was known as the Fancher party after Alexander Fancher, who led it.
It continues: "Col Dane-Maj Higby and me - on orders from Pres Young thro Geo Smith took part - I trust in God - I have no fear - Death hold no terror."
The massacre occurred as Utah's Mormons prepared for an invasion by federal troops, who had been dispatched to suppress the theocracy established in the region a decade earlier.
As the settlers' convoy entered the state en route from Arkansas to California, rumours spread that it contained men who had killed a Mormon leader. Church leaders vowed vengeance.
After a five-day siege the Mormon militia sent in a party under a flag of truce and promised safe passage. When the "gentiles" left their encampment all but the youngest children were killed.
The possibilities of a forgery or a false claim by Lee have not been ruled out, but experts said that at the time it was not unusual for people who wanted to preserve a record to etch it on lead.