Shashi Singh, BJP MLA Kuldeep Singh Sengar's close aide was sent to four days police custody on Monday.
On Saturday, agency also detained a woman, Shashi Singh, an aide of Kuldeep Singh Sengar in connection with the rape case. She allegedly took the victim to Sengar on the day of crime.
Sengar has already been arrested by the CBI in connection with the alleged rape of 17-year-old-girl in Uttar Pradesh's Unnao district.
The CBI had already registered three cases against Sengar in regard to the crime he allegedly committed last year. An FIR was lodged against the BJP MLA on Thursday under sections 363 (kidnapping), 366 (abduction of woman), 376 (rape), 506 (criminal intimidation) of the Indian Penal Code (IPC) and Protection of Children from Sexual Offences (POCSO) Act, and the case was handed over to the CBI, reported ANI.
The victim's family had also alleged that the accused MLA's brother, Atul Singh Sengar, along with his companions also raped the girl and thrashed the victim's father on April 3 for refusing to withdraw the FIR over the same. The father of the Unnao rape victim later died in judicial custody, reported news agency.