Carcasses of 31 monkeys were found buried in Saiyyad block on Friday and the remaining carcasses were found from Jagner and Jheejan areas of the tehsil, they said.
Sub-Divisional Magistrate Khairagarh Ram Singh Gautam said that post mortem of 27 monkeys revealed that they were poisoned while the other carcasses have been sent for post mortem.
An FIR in this connection has been registered on Friday based on a complaint by UP Forest department ranger Dal Chand Sharmaon at the Saiyyan police station against unidentified persons under relevant sections of the Prevention of Cruelty to Animals Act, 1960.
Environmentalist Shravan Kumar Singh said that the monkeys could not have died on their own and buried.