The CBI registered three separate cases related to the alleged rape of a woman by a BJP MLA and his brother, officials said.
Banagarmau MLA Kuldeep Singh Sengar is being questioned by CBI officers.
The victim had tried to immolate herself outside the residence of Chief Minister Yogi Adityanath triggering a massive political row over women's safety in Uttar Pradesh.
Later, the state police had arrested her father who died in judicial custody with the autopsy suggesting several injuries on his body.
A purported video of the girl's father before his death has also gone viral and was aired by several TV news channels. In the video, he alleged that he was mercilessly beaten up by the MLA's brother and others in the presence of police.
The Uttar Pradesh government had referred the matter to the CBI which registered the case after getting reference from the Centre last night. A notification was issued by the Personnel Ministry following a request for a CBI probe.