FIR has been lodged with Ayar police station against ex-minister Bhagwan Singh Kushwaha, a former mukhiya Nathuni Yadav and his two sons, Deputy Inspector General of Police (DIG) Shahabad Ajitabh Kumar said.
The FIR was registered on the statement of the deceased's father Gupteshwar Singh, the DIG said adding the ex-minister has been named a conspirator in the case.
No arrest has been made so far, the DIG said adding the reason behind the killing was yet not known.
The deceased was heading the Bhojpur district unit of Akhil Bhartiya Rashtriya Kisan Mahasangh (ABRKM), a body of upper caste landlords.
The opposition RJD today demanded a CBI inquiry into the killing of the Gram Panchayat chief.