A neighbour who raised the alarm said he witnessed the couple treating the girl like an animal, forcing her to eat pig feed and pull a horse-cart on which they were sitting.
Milenko and Slavojka Marinkovic were arrested at their home in a village in the northwestern Tuzla region after police received the tip-off from neighbour Sead Makalic.
“They kept her locked up, neither allowing her contact with other people, nor to go to school,” police spokesman Admir Arnautovic told FTV public television.
“They subjected her to inhumane treatment and torture.”
The couple were arrested on May 17 but police on Sunday said they could not reveal further details of the case, while prosecutors were not available for comment.
The girl, who has not been named, had been placed in a safe house and was receiving medical treatment, investigators quoted by FTV said.
Makalic said he remembered the German girl appearing in the village of Karavlasi but did not take much notice of her arrival.
“At the time I was helping them (the couple) to build their house and I did not pay attention,” Makalic said.
Years later, he said he saw her eating pumpkin and corn grains used to feed the couple’s pigs. One day, he said, he saw them make her pull a horse-cart “while they were sitting on it”.
“They put her in place of the horse and were laughing,” he said.
According to Makalic, the couple were from a “Roma family in which several brothers lived together, often travelling to Germany and Austria.
He said he had tried to alert police earlier. “But when the police came they hid her very well,” he said.
Earlier this year he had not seen her for about a year and was told by the couple that she was in Germany.
But “when I saw her again on May 15, I took a picture of her with my mobile telephone and went to alert the police”, he said.
Local media reported that the girl had arrived in Bosnia from Germany eight years ago with her mother, identified only as Kristina, and that she married Milenko Marinkovic to help him obtain a residence permit in Germany.
The mother has lived between Karavlasi and Germany for several years and was in the village at the time of the arrests, media reports said.
Local newspapers reported allegations of sexual abuse, quoting neighbours saying they heard the girl screaming and crying.