Abhinash Choudhury, 47, the mastermind behind the child sacrifice, is an ex-serviceman. He was arrested along with his accomplice Das, 52, the police said.
Both the occult practitioners have confessed to the crime by revealing to the cops that they killed the boy on Tuesday last to attain super natural powers.
The duo had picked up the boy as a soft target for the ritual as they were known to his family.
The accused slit the throat of the victim by a sharp-edged weapon and after killing him, they collected the human blood to use it later in a sacrifice ritual, the police said.
Ex-serviceman Choudhury, a father of two, got himself involved in occult practices after his retirement.
The Police stumbled upon books on Tantric cult during a search of his house. Neither his spouse nor the children were aware of Choudhury's black magic practices, they said.
The blood-stained body of class IV student Rajesh Nayak had been retrieved from the Luna riverbed on Tuesday evening.
Angry people yesterday protested by demonstrating and setting on fire the house of one of the occult practitioners.
