The federal courthouse in Brooklyn provided a bland judicial setting for some startling testimony this week, as former members of Nxivm, a self-improvement and wellness group that was allegedly a sex cult, described how devotees were manipulated to the point of enslavement to the group’s founder, Keith Raniere.

A case which on the surface contained the compelling components of wellness, self-improvement, celebrity and wealth was quickly reduced to accusations of base criminality.

The lone defendant, 58, has pleaded not guilty to seven counts of sex trafficking, possessing child abuse images and other crimes. In court he sat expressionless, stripped of whatever power he once had as head of a group in which he was known as “Vanguard”. Among Raniere’s alleged crimes is the forced branding of “sex slaves” within a clandestine sorority known as DOS, or “Dominus Obsequious Sororium”, Latin that roughly means “master of the obedient female companions”.

The prosecution’s first witness, a 32-year-old woman with an accent suggestive of Britain, was identified only by her first name, Sylvie. She described how she bonded with the Nxivm member Clare Bronfman, the Seagram liquor heiress, over a shared interest in competitive showjumping.

Bronfman, she said, offered to help bring her horse to the US so Sylvie, then 18, could improve her riding. That was around 2003, a time when, she said, she “didn’t have a strong sense of my own direction”.

Over time, Sylvie told the court, she began to feel dependent on Bronfman. She was introduced to Nxivm. Soon her thoughts turned to restricting her intake of food, an obsession common to many female members.

Her tale grew darker. She was encouraged, she said, to compete in a run during “V-Week”, a celebration of Raniere’s birthday. Then she was brought into the coveted top tier of women around Raniere: DOS.

Sylvie avoided being branded with Raniere’s initials but she described how during one ritual she was forced to wear a “dog collar”. Raniere, she said, pushed her to send him “vulnerable” photos of herself, until “literally, in the end, they were just of my vagina”.

Keith Raniere, centre, seated between his attorneys during the first day of his trial on 7 May. Photograph: Elizabeth Williams/AP

She was ordered to seduce Raniere, she said, by her “slave master”, a woman named Monica Duran. Raniere performed oral sex on her, she said, and she faked orgasm so he would stop. Afterwards, Sylvie testified, Raniere told her “he was my grand master now and that he was a master of Monica”.

By the end of her involvement with the group in 2013, Sylvie said, “everything was just lies and deceit and darkness”.

Such testimony will probably be repeated in a trial which could last up to six weeks. Some of Raniere’s alleged “slaves”, as well as members of his inner circle who pleaded guilty and agreed to cooperate with prosecutors, are expected to speak.

In addition to Bronfman, witnesses may include the former Smallville star Allison Mack, Nxivm co-founder Nancy Salzman and three daughters of a Mexican family. Raniere is alleged to have begun a sexual relationship with one sister, named in court as “Virgin Camila”, when she was just 15. Raniere has also been accused, though not charged, of raping a girl hundreds of times when she was 12 and 13.

‘Broken people’

As the case against Raniere unspools, larger questions may emerge, including how a group which appears to have begun as relatively benign program linked to the personal wellness movement could have developed into a hierarchical organisation of interlocking subgroups focused on sexual gratification and under the control of a single leader.

“I’m not surprised that a cult has sprung out of the wellness movement,” the psychologist Michael Langone, an expert on cults, told the Guardian. “But you have to have the same qualities as a cult that springs from any religious or political movement: the centralisation of control, a belief system vulnerable to critical scrutiny and an attempt to change people in fundamental ways.”

They joined because somebody said they had answers to life questions. In the process they became controlled Robin Boyle-Laisure

Samia Shoaib, an actor who says she was approached by Mack to join Nxivm, said: “It’s the perfect storm, where you get vulnerable people going to seek help from unregulated self-help practitioners.”

Many Nxivm members, she said, “had all the money in the world and were in a search for life-meaning. It may not be against the law to take advantage of someone’s unhealed wounds, but he [Raniere] found broken people and broke them some more, with the promise of fixing them.”

By focusing on human trafficking statutes and by arguing sexual or financial gain was central to Nxivm, prosecutors may have avoided a problem in cases against alleged cults: the difficulty of proving illegality around issues of consent and mind control.

“Cults grab headlines,” said Robin Boyle-Laisure, a law professor at St John’s University who has written extensively on cults. “But there’s nothing illegal about a cult. What can be illegal are the crimes these type of organisations can commit, including in this case the statutory rape of a minor.”

The existence of a cult around Raniere, Boyle-Laisure said, would not necessarily mean that a wellness group like Nxivm, which tapped into modern obsessions such as wellness, celebrity, affluence and thinness, was inherently dangerous.

“I don’t believe people joined the group saying ‘I want to look thinner,’” she said. “They joined because somebody said they had answers to life questions. In the process they became controlled about how to look and behave.

“That is what is so deceptive about cults. The engagement is not clear at the outset, people get sucked in, turn over collateral and then it’s too late to exit.”

‘A horrible evil’

Nxivm established a system of hierarchical groups or “modules”, including Jness (meant to help women “get a sense of their own essence”); the Society of Protectors (for men); and “executive success programs” with grandiose names, such as Compassion and Civilization. In Brooklyn, jurors heard how Nxivm groups and courses were costly to join, ranging from $6,000 to $10,000.

A former member, Marc Vicente, described a “12-point mission statement” that included phrases such as “I will not choose to be a victim” and “tribute is a form of payment and honor”. The document was “veneer” that covered “a horrible evil”, he said.

Keith Raniere interviewed by Allison Mack in a YouTube video. Photograph: YouTube

Hierarchical structures like that described in court this week are common to cults of any description. According to Jamieson Webster, a psychoanalyst based in New York, borrowings from the $9bn wellness industry gave Nxivm a contemporary, jargon-heavy flavor that spoke to followers in the same way eastern philosophy-tinged groups like Bhagwan Shree Rajneesh, latterly known as Osho, did in the 1970s.

“Self-help, some kind of ruthless economic agenda, and cultish group behavior travel hand-in-hand,” Webster said. “It’s a system that leads you further and further into it. Sure, they added the sex part in, but that was always there. It’s the same as Osho if you take the Indian spiritual veneer off it.”

In opening statements, counsel for Raniere argued that relationships within Nxivm were consensual, that the use of intimate photographs as “collateral” was merely proof of commitment and that control he placed on his “slaves” was in fact required by them.

“It’s a fine line between someone who can tap into this deep need and someone’s willingness to surrender to it,” said Webster. “It happens every time you buy a $12 green juice to purify your blood – it reveals a deep need for direction and meaningfulness.

“There’s nothing wrong with a self-help workshop, but people who are attracted to change and being changed are vulnerable to the kind of leader we see in cult situations – manipulative, interested in control and highly narcissistic.”