The deceased identified as Jatin Sharma had gone missing on Thursday evening while playing outside his house in East Rohtash Nagar area.
According to the police, the accused allegedly abducted the minor from outside his house and then took him to Rathi mills. They then strangled him to death, dug a grave and buried the boy with gunny bags atop.
"Meanwhile, the accused went back to their houses and in fact also helped the deceased's family search for the missing boy.
At 2 AM on Friday, the father of the deceased Chander Shekher Sharma received an SMS from an unknown number demanding Rs 30 lakh for the boy's safe release.
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The investigators managed to track the mobile phone used for sending the SMS using technical analysis.
"It was found that the kidnappers belonged to Shahdara. We managed to zero-in on the owner of the mobile. It was in the name of the juvenile's father," said the officer.
Some friends and classmates of the deceased had seen Jatin with the juvenile accused.
"The body was recovered from an abandoned site in Rathi mill on Friday evening.
"The juvenile has been sent to the juvenile justice home, while the other accused person was arrested.