The victim's mother has alleged in the complaint given to the Uttar Pradesh Police, which is now part of the CBI FIR, that the woman lured her daughter to the MLA after which he raped her.
She has also alleged that while the MLA was raping her daughter, Shashi Singh stood outside the room as a guard.
The agency arrested Sengar, the prime accused in the case, last night after 16 hours of questioning at its office in Lucknow.
The CBI has taken over the investigation in the three cases related to the alleged rape of the 17-year-old girl by Sengar.
A CBI team visited the crime scenes in Makhi village in Unnao district and talked to the victim's family, witnesses and officials of the hospital where the victim and her father were taken for treatment.