Clare Bronfman competes in the 2004 Bayer/USET Festival of Champions, Presented by State Line Tack at the Del Mar Fair Grounds in Del Mar, California. (Photo by Tim Tadder/Corbis via Getty Images

In the summer of 2013, with his health failing, the billionaire businessman Edgar M. Bronfman was visited at home by his youngest daughter, Clare. She brought with her a production crew that was making a film about a self-help group called Nxivm.

Mr. Bronfman, the former chairman of Seagram Company, had long clashed with Clare and her sister Sara over their lavish financial support of the group. A decade earlier, they had given $65 million of his liquor fortune to its leader, Keith Raniere — money that he promptly lost in the commodities market. Soon afterward, Forbes published a critical article about Mr. Raniere in which Mr. Bronfman described Nxivm as a "cult."

But Clare Bronfman had not come on that day in 2013 to make peace with her father, who died later that year. Instead, she pressed him to admit on camera that he had been wrong to criticize Mr. Raniere, said a former Nxivm official who was present at the meeting.

"He was very sick," said the official, Mark Vicente. "He appeared to be very saddened by her questioning."

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Last fall, Nxivm (pronounced Nex-e-um) started to unravel after The New York Times reported that women who were part of a secret sorority within the group were branded with a symbol that contained Mr. Raniere's initials. Attention around Nxivm was stoked by the involvement of various rich offspring and minor celebrities, including the "Smallville" actress Allison Mack. In March, Mr. Raniere was charged in federal court with coercing women into having sex with him by threatening to reveal damaging personal secrets they had disclosed in order to join the sorority.

Prosecutors in Brooklyn said at the time that other Nxivm members were likely to be indicted too — and on July 24, Ms. Bronfman, 39, was among several executives charged with conspiracy and criminal racketeering. Her transit from heiress to criminal defendant, interviews and court filings suggest, appears to be the story of a child of privilege who fell under the spell of a beguiling manipulator who offered power, a sense of purpose and the possibility of love. The ferocity with which she embraced Mr. Raniere and Nxivm makes her case even more singular.

Ms. Bronfman, who never attended college, served in recent years as Mr. Raniere's legal Torquemada, financing and aggressively pursuing long-running lawsuits against Nxvim's enemies, both real and perceived. She filed criminal complaints against defectors from the group; used lawyers to threaten its critics; and allegedly hired an investigative firm in Canada as part of an ill-fated plan to hack into the bank records of American judges and politicians, according to interviews, court filings and previously published accounts. Many of those who spoke did so anonymously because of privacy concerns, or because prosecutors had asked them not to discuss the case publicly.

In the indictment, Ms. Bronfman is accused of identity theft in order to access other people's computers; of money laundering to abet the entry of an alien into the United States; and of improperly paying off the credit card of Mr. Raniere's dead girlfriend, so that he could continue to use it after her death. (Ms. Bronfman did not respond to numerous emails seeking an interview, and her lawyer, Susan R. Necheles, also did not respond to emails.)

Ms. Bronfman's arrest was astonishing in part because of the Bronfman family's standing in New York business and philanthropic circles. Her father was a major benefactor of Jewish organizations, and several of the five children from his first marriage have had high-profile careers. A son, Edgar Bronfman Jr., once served as chief executive of Warner Music.

Sara and Clare Bronfman were born to their father's third wife and are 20 years younger than some of their half-siblings. After their parents divorced, when they were 7 and 4, they left New York and grew up in Kenya and England, according to a 2010 article in Vanity Fair.

It was Sara Bronfman who introduced her sister to Nxivm in the early 2000s. The group, which was based in Albany, N.Y., offered its members workshops that it said were designed to help participants achieve greater self-fulfillment by removing emotional and psychological roadblocks.

At the time, the Bronfman sisters, who were then in their early 20s, were opposites in both appearance and personality. Sara was blond, outgoing and likable, and appeared to be seeking a direction in life. Clare, who is extremely thin and has a narrow face and brown hair, struck Nxivm members as dour and socially awkward. She also already had a passion. As a teenager, she had become an equestrian, going on to compete in international events and open a farm to train horses.

At first, Clare Bronfman appeared to have little interest in joining Nxivm. But several meetings with Mr. Raniere turned her into a believer. She also apparently fell in love with Mr. Raniere, who had sexual relationships with many Nxivm women, several former members said. Starting in the late 1990s, approximately 16,000 people took his courses, and some were drawn deeply into the group, giving up careers and past ties to become followers of Mr. Raniere, who was referred to as "Vanguard."

In the early 2000s, Edgar Bronfman Sr. also took some Nxivm training courses, before quickly losing interest. Several former Nxvim members said that Mr. Raniere was convinced that the businessman was behind the negative Forbes article about him. He blamed the Bronfman sisters for the episode, those former members said, and used it to exert control over them.

In the mid-2000s, Edgar Bronfman Jr., while he was head of Warner Music, also apparently once came to Albany at the request of his sisters to help judge a Nxivm-sponsored a cappella singing contest, said several people familiar with his visit. (Mr. Bronfman did not respond to emails seeking comment.)

As Clare Bronfman's authority within Nxivm grew, she did not hesitate to wield it, several former members of the group said. When people she hired to work for her asked for higher pay, for example, the heiress said no and lectured them about appreciating the value of money.

"I found her very degrading and very reprimanding," said one ex-Nxivm member, Bonnie Piesse, who is married to Mr. Vicente, the former Nxivm official who witnessed Ms. Bronfman interviewing her father about the group. "She was very cold."

Nxivm was based in Albany, N.Y., and attracted thousands to its self-help courses. Some were drawn deeply into the group, giving up careers and past ties to become followers of its leader, Keith Raniere.

For more than a decade, the Bronfman sisters used their substantial fortunes to underwrite Nxivm in a variety of ways. To raise Mr. Raniere's profile, they arranged for the Dalai Lama to visit Albany. The group made use of a private jet they provided to ferry celebrities it was courting as recruits. Clare Bronfman also bought an island in Fiji that Mr. Raniere and other Nxivm officials used as a retreat.

Sara Bronfman eventually married and had children, and her involvement in the group diminished. But Clare Bronfman's singular focus stayed on Mr. Raniere and Nxivm. Along with financing the organization, she started two nonprofit organizations to promulgate its ideas.

One of them, the Ethical Science Foundation, conducted a study to see if Nxivm's training techniques could be used to treat people with Tourette's syndrome, a disorder marked by involuntary tics or verbal outbursts. A Nxivm-affiliated doctor associated with that study also carried out a bizarre experiment in which female followers of Mr. Raniere were shown films containing scenes of extreme violence while their facial expressions were videotaped.

It is not known whether Ms. Bronfman was aware of that study and, if so, whether she approved of it. But none of the recent revelations about Mr. Raniere or Nxivm's practices appear to have shaken her belief in the group.