The nine U.S. citizens who were killed in a brutal ambush by drug cartel gunmen Monday while traveling in Mexico belonged to a Mormon offshoot group that has been touched by cartel violence before.

The group was part of the extended LeBaron family, Mormon fundamentalists who first came to Mexico nearly a century ago — when the Church of Jesus Christ of Latter-day Saints in Salt Lake City started cracking down on members who were still practicing polygamy.

To escape persecution in the U.S., Alma Dayer LeBaron brought his wives and children across the border to Mexico in 1924 and founded the LeBaron colony in the Mexican state of Chihuahua.

To escape persecution in the U.S., Alma Dayer LeBaron brought his wives and children across the border to Mexico in 1924 and founded the LeBaron colony in the Mexican state of Chihuahua.

It was there in 2009 that drug cartels held Eric LeBaron, a teenager in the family, hostage for ransom. While Eric was released unharmed even though the ransom was not paid, cartels later murdered his brother, anti-crime activist Benjamin LeBaron, who had led a protest to secure Eric’s release.

An empty classroom in Colonia LeBaron in Chihuahua, Mexico, in 2009. Adriana Zehbrauskas / NYT via Redux file

Anna LeBaron, Alma Dayer LeBaron's granddaughter, told NBC News that she did not personally know the nine victims who were killed this week, but she said other family members confirmed they were LeBaron relatives, and said the whole family was "heartbroken."

Over the years, members of the extended LeBaron family have spread throughout northern Mexico as well as into Arizona and Utah, according to Matthew Bowman, a historian and author of “The Mormon People: The Making of an American Faith.”

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The family has had a sordid history, Bowman said. Its founder's sons fell victim to infighting. One, Ervil LeBaron, formed his own church that took on a cult following, said Anna LeBaron, who was one of Ervil's 51 children with 13 wives. She was born at the LeBaron colony and escaped her father's cult when she was 13; she detailed her experience in a 2017 book, "The Polygamist's Daughter."

The cult was disbanded in the early 1990s and her father died in prison in 1981 while serving a life sentence for murder.

"My father would order mob-style hits and those would be carried out by his cult members if they stopped believing in him or his practice or religion and left, or sometimes it was rival cult leaders that were blood-atoned for being false prophets," she said, adding that media outlets dubbed him the "Mormon Manson."

But Anna LeBaron was quick to add that none of the LeBaron family's dark past seems to be connected to Monday's killings, which Mexican Security Secretary Alfonso Durazo said may have been a case of mistaken identity, with a drug cartel possibly mistaking the convoy of large SUVs the family was traveling in for rival gangs.

An army car patrols the street in Colonia LeBaron in Chihuahua, Mexico, in 2009. The government sent soldiers and state police to protect the town after a gunmen killed a Mormon anti-violence activist. Adriana Zehbrauskas / The New York Times via Redux file

While the LeBarons' fundamentalist offshoot group is distinct from the Church of Jesus Christ of Latter-day Saints, there are many Mormons in Mexico, said Paul Reeve, Simmons professor of Mormon studies at the University of Utah. The Salt Lake City-headquartered church currently claims over a million members there.

Mexico was friendlier to polygamy in the past, with a law on the books prohibiting it when the United States banned it in the 1880s but with a "president at the time who basically agreed to look the other way," but the members of the Church of Latter-day Saints who are in Mexico have since abandoned polygamy, Reeve said.

There generally has not been a history of violence targeting Latter-day Saints, Reeve added, although there was an overall anti-American sentiment during the Mexican revolution from 1910 to 1920.

In response to Monday's killings, Eric Hawkins, a Latter-day Saints Church spokesman, said in a statement: "We are heartbroken to hear of the tragedy that has touched these families in Mexico. Though it is our understanding that they are not members of The Church of Jesus Christ of Latter-day Saints, our love, prayers and sympathies are with them as they mourn and remember their loved ones."

CORRECTION (Nov. 11, 2019, 5:15 a.m. ET ): A previous version of this article misstated the circumstances surrounding the death of Benjamin LeBaron. He was killed after protesting the kidnapping of his brother, Eric; he was not kidnapped himself.