An eighth-grade boy was found hanging from the fan of his classroom in Khulna's Dumuria upazila early Friday, the day after he was reported missing, police said.
Six people were detained in connection with the incident.
Nirob Mandal, 14, from Gutudiya village of the upazila, was a student of Gutudiya Secondary High School.
Locals and police said Nirob did not return home after attending school Thursday morning.
Family members looked for him everywhere but could not find any trace of him.
An anonymous person called Nirob's father Shekhar Mandal over the phone and demanded Tk30 lakh as ransom in the afternoon, they said.
After that, Shekhar Mandal lodged a general diary at the police station.
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Sheikh Kony Miah, officer-in-charge (OC) of Dumuria Police Station, said on information they found the body hanging inside a classroom around 1am. However, he did not say how they were tipped off to the classroom.
"It was assumed that Nirob's body was hung from the ceiling fan after he was strangled to death. The body was sent to Khulna Medical College Hospital for autopsy," the OC added.