An Iranian man posed as an oil tycoon with contacts in the fashion industry to lure young women to his Marbella mansion where he subjected them to years of sexual slavery.
Sources close to the investigation have told the Spanish media that the man fathered seven children with the women, who are aged between 19 and 24.
It is alleged that the women were subjected to psychological and emotional abuse that left them too scared to leave the house in the luxury Spanish resort.
"He enjoyed their company whenever he wanted," a source close to the investigation told Spanish daily AS.
"They were always controlled and supervised by him. He threatened to harm them if they didn't tell him everything they were doing."
The source added that the man, whom media have named as Shoja S, 50, forced his victims to hand over money to him regularly.
One of the women has filed a lawsuit against 50-year-old Shoja S for allegedly forcing her family to pay the €6,500 (£5,300) monthly rent for the Marbella mansion.
Eight others have now filed charges against him for physical and psychological abuse.
The woman are originally from Germany, Lithuania, Kazakhstan, Denmark, Mongolia, Russia and Turkmenistan.
Some are now living in shelters, and one has left the country.