The letter threatening to kill the top district officials was received on Saturday and prima facie it does not appear to be sent by Naxal or any other organisation, DIG, Rajesh Kumar Srivastava said.
In the preliminary inquiry, it appears to be the mischief of some local person and efforts are on to trace him, he said.
After the letter was received, the SP, Balikaran Yadav had alerted all the police stations and directed for thorough checking.