A Bulgarian couple suspected of being the biological parents of Maria, the young girl found in a Roma community in Greece, have been questioned by police.
Officials said they had taken DNA samples and were investigating whether the woman had sold the child, a crime that could result in a jail sentence.
The couple have been named by Bulgarian media as Sasha Ruseva and Atanas Rusev, from the central town of Nikolaevo.
A woman believed to be Ms Ruseva has admitted giving up a baby in Greece.
But she denied to Bulgarian TV reports that she had received payment for the girl four years ago.
She could not say for definite that Maria was hers, but said she burst into tears when she saw the girl on news reports. Maria bears a striking resemblance to some of her other children.
Maria came to the Greek police's attention after they raided the Roma camp near Farsala in central Greece last week.
They were initially searching for drugs and weapons, but noticed the lack of resemblance between the blonde-haired, green-eyed, pale-skinned little girl and her parents. They found further discrepancies when they investigated the family's documents.
The couple, Christos Salis and Eleftheria Dimopoulou, have since been charged with child abduction. They have insisted the girl was given to them legitimately.
'Never took money'
The couple believed to be Sasha Ruseva and Atanas Rusev, and their eight children, were filmed by Bulgarian television at their home in the Roma district of Nikolaevo.
Ms Ruseva, holding a child with red hair, told reporters that she and her husband had been working in the Greek town of Larisa four years ago when she gave birth to a girl.
The girl was seven months old when they had to return to Bulgaria, and she said she could not afford to take the child with her.
She said she was talking to a woman she worked with who told her: "Give me this child, I will take care of it. You can come and take it back anytime you want.
"But I had other children to take care of and I couldn't go... I have never got any money for it."
Bulgarian officials said that during questioning, Ms Ruseva said she recognised Christos Salis and Eleftheria Dimopoulou as the people she left her child with.
Prosecutors announced they had pressed preliminary charges against Ms Ruseva for "deliberately selling a child while residing out of the country".
"A DNA test has been taken from Ruseva, and information has been collected about her trips to Greece in the last years,'' said a statement from the prosecutor's office.
Greek news site zougla.gr earlier published what it said was the identity card of Ms Ruseva and a birth certificate for Maria from a hospital in Lamia, not far from Farsala and Larisa.
The birth certificate says the girl was born in January 2009.
Christos Salis and Eleftheria Dimopoulou told police Maria was four years old, but the Smile of the Child charity say medical examinations suggest she is more like five or six.