The incident occurred in the morning when P. Venkara Rao, who was sleeping in an agricultural field to guard crops, was taken away by the Maoists and was shot dead, police said.
The Naxals left a letter stating that Rao had worked as police informer earlier. The murder was committed by the ultras only to establish their presence in the area, they said.
"The Maoists killed an innocent, illiterate tribal only to establish their existence. The deceased had no idea even to operate a mobile phone. He was very poor and did not own land," Vizianagaram district SP Navdeep Singh Grawal said.