The public prosecutor's office in Bochum is investigating a man who is said to have raped a woman who fled to North Rhine-Westphalia from the Ukraine.
The suspect from Herne has been in custody since March 18, a spokesman for the authorities said on Thursday.
The "Kölner Stadtanzeiger" had previously reported on the case.
The 25-year-old is said to have been sexually abused by the 43-year-old.
She and her son lived with him after they escaped.
Both came into contact through a private offer of accommodation.
The victim was able to contact relatives via cell phone, who then alerted the police.
The investigations were ongoing.