The powerful pipe bombs that killed two people and maimed a third here last week set off more than a murder mystery. Those bombs, which exploded virtually in the shadow of the towering Mormon Temple, have transfixed the large and thriving community here that belongs to the fastest-growing branch of world Christianity: the Church of Jesus Christ of Latter-day Saints.

Although police have no clear explanation of the violence, they say their "prime suspect" is Mark Hofmann, a 30-year-old Mormon and collector and trader of antiquarian documents. Today, police arrested a reported business associate of Hofmann's, Shannon Patrick Flynn, 27, and charged him with illegal possession of a machine gun. Authorities said evidence related to the bombings was found at Flynn's condominium.

Hofmann was already a figure of some notoriety in this religious capital because he had obtained and made public an 1830 letter -- known as the "white salamander letter" -- that offers a partially new gloss on the founding of the Morman faith by the prophet Joseph Smith Jr. early in the 19th century. Hofmann sold the letter to another Mormon, Steve Christiansen, who was one of the two victims of last week's pipe-bomb explosions.

The letter differs only slightly from official accounts of the church's beginnings, but it was anathema to some Mormon leaders because it suggests an atmosphere of necromancy and magic about the origins of the faith. And the Mormons, acutely aware of the ridicule, persecution and legal discrimination they suffered for decades, are determined to show that their faith is firmly rooted in historical truth.

Far more than Baptists, say, or Presbyterians, the Mormons, who count their church's lifetime not in centuries but in decades, are intensely aware of their history. "History has always been central to Mormonism," wrote the Yale historian David B. Davis, "as a foundation of faith, a source of group identity and a vulnerable target . . . for attack."

On the surface, it would seem the church leaders need no longer worry about outside attacks on their faith.

The "restored" Christain faith that Smith built has grown into a thriving church with 5.8 million members worldwide and some 200,000 converts annually. The church has a global welfare program, a prospering business empire and, in the western United States, at least, considerable political clout.

In a secular age, Mormons on the whole are a devout, happy religious people; they have far lower rates of divorce, illegitimate birth, alcoholism and criminal behavior than the general population.

As befits a religion founded by a New Yorker named Joe Smith, the Mormon Church is an intensely American faith. Some early Mormons received a divine revelation that the Garden of Eden was in Jackson County, Mo. The remarkable book at the core of the faith, The Book of Mormon (subtitled "Another Testament of Jesus Christ"), is an American history.

"And it came to pass, as they understood they cast their eyes up again towards heaven; and behold, they saw a Man descending out of heaven; and he was clothed in a white robe . . . he stretched forth his hand and spake unto the people, saying: Behold, I am Jesus Christ . . . . "

This remarkable scriptural passage, depicting the visit of Jesus Christ to the American Indians shortly after the resurrection, is the climactic moment of The Book of Mormon, a supplemental Bible for members of the church.

The Book of Mormon tells the story of ancient Israelites who crossed the Atlantic about 600 B.C. and settled in America, where they practiced the religion of Moses. In the first century A.D., the risen Christ came to them, healing the sick and organizing a church in his name.

Mormon documents tell that the immigrant Israelites compiled a record of these events and buried it in a hill in upstate New York; that the record was revealed by the angel Moroni in 1823 to a young farm boy named Joseph Smith Jr.; that with divine aid Smith translated the history, producing what is now called the Book of Mormon.

The story of the 19th century Mormons' battles against ridicule and persecution, of Smith's murder by an angry mob and of the resulting exodus in which the "American Moses," Brigham Young, led thousands of Mormons to walk across mountain, desert and plain to found a "New Zion" by the shores of Great Salt Lake, is one of the great epics of American history.

But to many Mormons, including the current leadership of the church, the threat of persecution is not just history.

The church leadership has been stung by recent demonstrations and governmental pressure against Mormon missionaries in foreign countries. And people throughout the faith are seriously disturbed by actions such as the recent decision by a community interfaith meeting hall in Colorado to exclude Mormons on the grounds that they are a "cult."

The desire to establish legitimacy as a significant branch of Christianity is one reason the church is so committed to historical proof of its scripture and doctrines.

But within the faith, too, there is a strong impulse to find a historic basis for church teachings. "We have our mysteries, but we don't celebrate the mysterious the way some faiths do," says Peggy Fletcher, publisher of Sunstone, a fairly liberal Mormon journal. "We want to get at the history that explains those mysteries."

Accordingly, a visitor to Temple Square, the 10-acre complex here that is the geographic soul of the church, can see many scholarly exhibits supporting the historicity of the Book of Mormon. For instance, there is a replica of an ancient reed boat like those constructed in the Middle East in Biblical times. The exhibit says that such boats could have carried the Israelites across the Atlantic to the New World.

The Mormons sponsor and publicize historical seminars and studies showing that pre-Columbian American Indians had a prevalent legend of a "white god" who came among them. "The Great White God . . . is Jesus Christ," declares a church publication, "Christ in America." The church has also striven mightily to establish the truth of Smith's story of how he found the buried record of the ancient Americans and translated it into the Book of Mormon.

Smith said an angel named Moroni -- the angel depicted in a gilded statue atop every Mormon temple -- led him to a collection of golden plates containing writing like hieroglyphics.

With the assistance of the angel, Smith wrote, he was able to translate the plates.

This is where the "salamander letter" comes in.

The letter, evidently written by Martin Harris, one of Smith's closest associates, says that a "white salamander" that transformed itself into an "old spirit" led Smith to the golden plates.

Mark Hofmann, who has made a career of finding and trading old Mormon documents, discovered the letter in 1984 and presented it to Mormon historians for authentication. In May of this year, two distinguished historians declared the letter authentic. Hofmann subsequently sold the letter to a collector here for $40,000.

The church leadership accepted the historians' determination but suggested that the letter might be a 19th-century forgery.

Two weeks ago, at a general church conference here, some elders spoke critically of people who dredge up materials challenging church doctrine. Hofmann reported to police that he received a death threat after that conference.

But the issue had settled down somewhat until Tuesday, when Steve Christiansen, the collector who had bought the letter from Hofmann, was killed by a pipe bomb. Kathleen Sheets, the wife of an associate of Christiansen was killed by a separate pipe bomb that day.

The next day Hofmann was badly injured when a similar bomb exploded in his car.

That led to police suspicion that Hoffman might have been the bomber, although no clear motive was established. Hofmann has so far denied any guilt.

There is also some suspicion among law enforcement officials that the "salamander letter" might be a forgery, despite the authentication this summer.

Today, the U.S. attorney here asked the Mormon Church, which owns the letter, to turn it over for investigation. The church agreed to do so.