The deceased was identified as Zahurul Islam, 13, son of Abdul Awal of East Ukilpara in Feni district town.
Getting no response from Zahurul's room, the other students of Hamida Sadia Mohila Madrasa peeped through the room's window and found Zaharul was hanging from a window grill around 5:15 pm, said Abul Kalam Azad, officer-in-charge of Feni Model Police Station.
On information, police recovered the body and sent it to local hospital morgue.
Police detained three teachers of the madrasa for interrogation, the OC added.
However, Amzad Hossain, paternal uncle of Zahurul, said Zahurul got admitted to the madrasa in January and he often claimed that the teachers of the institute used to torture him.
Claiming that Zahurul couldn't commit suicide, his uncle said the boy was tortured to death.