The agency which was referred the matter only yesterday took immediate action by re-registering the UP police FIRs and brought the four-time MLA to its Lucknow office at around 5 am for questioning, they said.
The officials said Sengar, an MLA from Bangarmau, had not been arrested yet.
They said a team of officials would visit the scene of crime and question jail officials, police officials and family members of the MLA.
The first FIR pertains to the alleged rape of the girl in which Sengar and a woman Shashi Singh have been named as accused.
The second one pertains to rioting, in which four locals have been booked, and also the alleged killing of the victim's father in judicial custody. Since the murder charge was added later by the police, it does not reflect in the CBI FIR.
The third case pertains to the allegations against the victim's father who was arrested under arms act and put in jail by the local police where he mysteriously died. He also suffered serious wounds as per the post- mortem report.
According to the rules, the CBI re-registers FIRs of the state police while taking over the probe but remains at freedom to come to its own conclusions which are filed before a special court in its final report. The final report can either be a closure report or a charge sheet.
The victim has alleged that she was raped by the MLA at his residence on June 4, 2017 where she had gone with a relative seeking a job.
In February, the girl's family moved court seeking to include the MLA's name in the rape case.
After filing of the case, the victim's father was booked by the police under the arms act on April 3 this year and put in jail on April 5.
Frustrated with the alleged inaction and coercion from powerful people, the victim attempted self immolation in front of Chief Minister Yogi Aditynath's residence on April 8 which made headlines.
The next day, her father died in jail with post- mortem suggesting serious injuries on his body.
Faced with the embarrassment of its own MLA from Bangarmau in Unnao allegedly being involved in the rape case, the state government had referred the matter to the Centre yesterday -- a day before Allahabad High Court was to pronounce its order on probe into the case by the central agency.
The Centre too acted with alacrity referring the matter to the CBI last night. The agency sleuths swooped down at the residence of Sengar in Lucknow in the early hours today and took him for questioning at its office in Lucknow, the officials said.
A purported video of the girls father before his death has gone viral and was also aired by several TV news channels.
In the video, he alleged that he was mercilessly beaten up, including with rifle butts, by the MLAs brother and others in the presence of police.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)