CBI sources said Raja Bhaiya was quizzed along with his cousin Akshay Pratap Singh, his confidante Hari Om Srivastava, Nanhe Singh, and his 'kothi' manager Laljee Niham along with three villagers.
The questioning is likely to continue tomorrow, the sources said.
The sources said 44-year old Raja Bhaiya appeared at CBI camp office at Kunda and was asked a number of questions in connection with the murder of villge head Nanhe Yadav and subsequent killing of the DSP.
Last month, CBI had arrested one Bhulle Pal, a security guard with the then state Minister Bhaiya who allegedly led a mob, enraged by the killing of Balipur village head Nanhe Yadav, to kill the police officer.
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Bhaiya has denied any association with Pal.
CBI has also taken into custody Rajeev Singh and Guddu Singh who are considered close to the minister.
In the FIR filed on the basis of a complaint by the slain DSP's wife Parveen Azad, it has been alleged that on the directions of Bhaiya, Nagar Panchayat Chairman Gulshan Yadav, Hari Om Srivastava, Raja Bhaiya's driver Rohit Singh and supporter Guddu Singh first assaulted her husband with sticks and rods and later shot him dead.