The Buenos Aires Yoga School operated in the Argentine capital for 30 years, recruiting vulnerable young women with a promise of "eternal happiness" and then sexually exploiting them, according to Argentine prosecutors.
They said the group, which they privately dubbed "Cult Inc", was a criminal organisation involved in sex trafficking, money laundering and involuntary servitude. There were no yoga classes.
Former members of the group alleged that women in it were called "geishas" and "slaves" and expected to have sex with guests at the 26-room school.
One former member, Pablo Salum, said children as young as 11 were made to watch orgies and expected to have sex at the direction of the group's leaders. He was brought into the sect by his mother when he was eight.
Wealthy men were matched to women
Wealthy and powerful men were matched to women in the group's "Geishado VIP" section.
Some of the women were sent to have sex in Uruguay and the United States, where the sect had property in Las Vegas, according to prosecutors.
The 84-year-old leader Juan Percowicz, known as The Angel or The Maestro, and 18 others were arrested in raids in August.
Domingo knew at least four leading members of the sect for years through musical connections. Two of them were well-known pianists and composers who had performed in the US.
One former member of the group, known as Carlos, told the Associated Press he saw Domingo visit the school several times in the 1990s.
That included once as the guest of honour at a dinner party, where he sat with classical musicians who were among the leaders of the group.
Domingo, 81, was drawn into the scandal after Argentine authorities released recordings of a taped phone conversation featuring the voice of a man they identified as the tenor.
He appeared to be arranging a meeting at his hotel in Buenos Aires with Susana Mendelievich, a concert pianist whom prosecutors say was a sect leader in charge of the Geishado VIP.
Tried to recruit Domingo
There was no evidence the meeting took place.
In a separate phone call, Mendelievich discussed with another sect leader how they had tried for years, but unsuccessfully, to recruit Domingo.
Spanish newspaper El Pais reported that she said in the call: "We’ve been trying for 30 years using these music [connections] and we still haven’t succeeded."
Mendelievich was also recorded asking Percowicz if she could take Domingo to "the museum".
That was the top floor of their 10-floor building in Buenos Aires where prosecutors allege men had sex with female members of the sect. There was no evidence Domingo went there.
Has not been charged
Domingo has not been charged and is not being investigated.
In the wake of the raids the tenor publicly distanced himself from the group. He told a television station in Mexico, where he was performing: "Of course, I have nothing to do with that."
He did not deny his was the voice on the recording but said he felt betrayed by musicians he had considered friends.
He said: "It makes me sad when you've had friends for many years and you realise you have been used."
In 1996 Domingo performed in front of 10,000 people at the Buenos Aires Polo Grounds.
He closed the evening with compositions by three members of the Buenos Aires Yoga School, one of whom was Mendielivich.
The La Nacion newspaper review at the time referred to it as an inferior composition.
Argentine Commissioner Ricardo Juri said the sect had sought to maintain its relationship with Domingo to "generate business".
He told El Pais: "Having Placido Domingo around was helpful."
Two years ago Domingo accepted "full responsibility" after being accused of sexual harassment by numerous women.
An investigation into his behaviour was carried out by lawyers hired by the American Guild of Musical Artists. He subsequently had concerts cancelled in the US but continued to perform in other parts of the world.
At the time Domingo said: "I am truly sorry for the hurt that I caused them.
"I understand now that some women may have feared expressing themselves honestly because of a concern that their careers would be adversely affected if they did so.
"While that was never my intention, no one should ever be made to feel that way."