The regional Sydöstran newspaper reported that the man, 31, and the woman, 30, had offered different accounts about what happened in their apartment on Walpurgis night. The man was a relative of the 8-year-old girl, who was found lifeless in the apartment. She was pronounced dead in hospital later.
The cause of death had still not been determined, but may be revealed on Tuesday, as the young girl's body has been sent to autopsy.
IN PICTURES: Karlskrona mourns as the police and the municipality investigate the 8-year-old's death
The police said it was still unclear who had called emergency services on the night of the girl's death.
Her death has stunned the town in southern Sweden with floral tributes left outside her school and her home. It has since emerged that social services were alerted to the girl's precarious living situation over a year ago.
Shortly before her death, a neighbour alerted the police to her suspicions that the girl was being abused. On Good Friday, she met the 8-year-old in the elevator of their apartment building and noticed that she was bruised and had problems walking. The police sent the complaint on to social services four days later, as the report coincided with the long Easter holiday weekend.
The girl came to Sweden by herself last year. The 31-year-old man and the 30-year-old woman were her legal guardians. The girl's parents found out about her death via Facebook, before the authorities in Sweden managed to liaise with police in Gaza to try to have an officer tell the family of the death in person.