The statement, delivered during the 150th anniversary commemoration of the massacre by descendants of the victims, expressed "profound regret" for the murders.

Turley said he and his co-authors approached Young's role "as a historical question, not as a theological or a political one. We were open to any possibility."

Much of what has been written in the past decade about Young's involvement relies on one or two theories, he said.

One theory says Young ordered the massacre to avenge the death of church leader Parley P. Pratt, who was murdered earlier that year in Arkansas. No evidence has been found in letters Young wrote around that time showing he sought to avenge Pratt's murder, Turley said.

The theory "requires the supposition that (Young) must have been seeking vengeance. But that runs contrary to the evidence," he said, adding it amounts to "little more than a personal statement of what the theorists believe. They can believe whatever they want, but personal belief is not the same as historical proof."

The second theory that Young ordered the murders is based on minutes of a meeting 10 days before the massacre between Young and Indian leaders from central and southern Utah. That meeting was "sketchily documented" in the journal of an Indian interpreter on whom Young relied, he said, and contains evidence that Indian leaders "declared themselves afraid to fight" Americans.

There is "no proof any of the Indian leaders in the meeting made it to Mountain Meadows or participated in any way" in the massacre, Turley said, or that the meeting precipitated the attack. "We do have evidence that many of them were still in the area of Salt Lake City around the time of massacre."

One Indian leader named Ammon did go to southern Utah after the meeting, "but he didn't arrive there until after they (the Fancher party) had been attacked," and had negotiated peacefully with the emigrants on his way south, Turley said.

The theories put forward by some that Young ordered the massacre include "untenable theses and strained arguments" that Turley said are not credible based on existing evidence.

Co-author Ron Walker, a recently retired professor of history at Brigham Young University, said his six years of research into the massacre have been a "dark and lonely place where no man should have to go."

Historically, genocide like that in the Holocaust, Rwanda, Armenia and South Africa has been preceded by the existence of several common characteristics, including demonizing the "other," authority, obedience, peer pressure, ambiguity, fear and deprivation. All those conditions were present in Cedar City at the time of the murders, he said.