The victim, Saiful Islam Tanim, is now undergoing treatment at Sitakundu upazila hospital.
Police arrested victim’s step -father Md Salauddin on Monday, said Abul Bashar, sub-inspector of Sitakundu Police Station.
Police said that Saiful is son of Yeasmin Akhter, 28, second wife of Salauddin, 46.
While marrying Yeasmin five years ago Salauddin accepted her son. After the marriage he used to torture the boy.
On Saturday morning, Salauddin asked Yeasmin over phone to send her son to the hill for collecting vegetables.
When, Saiful went there, Salauddin beat him up mercilessly with a stick, leaving him critically injured.
When the boy returned home, his mother found severe injury marks on his body.
Dr Nuruddin Rashed, upazila health officer, said that treatment is underway and it will take time for his full recovery.
Yeasmin filed a case in this connection, said the police official.
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