The body of Vishnu Raj Kumar, a Class 6 student of Don Bosco School, was found in a Sarsar village orchard. Mufassil police suspect he was killed a day after his kidnapping on Wednesday.
Kumar's father Raj Kumar Prasad, a resident of Naya Bazaar area in Bailhatta, received a ransom call from the abductors on Wednesday asking for Rs 30 lakh for the boy's safe release.
A distraught Mr Kumar, who is a trader, says prompt police action could have saved his son.
"My son was kidnapped when he was on way to my shop located in Shaddanand Bazaar in Siwan town. We informed the police but no action was taken till Thursday.
After the boy's body was found, hundreds of angry people blocked roads and demanded action against the police officer in-charge.
Siwan Superintendent of Police Saurav Kumar Sah assured that the culprits would be arrested.
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