Police recovered the body of a six-year-old boy from Rakhal Buruj Ghat of Karotoa River in the district yesterday.
The victim was identified as Nurunnabi, son of Phul Mia of Sonarpara village in Gobindaganj upazila.
Police said, one Ratan Sarker at Miapara village kidnapped Nurunnabi on Saturday and demanded Tk 50,000 as ransom.
However, victim's father refused to pay the ransom and instead filed a case with Gobindaganj police station accusing Ratan and three others.
Angered by the incident, Ratan killed Nurunnabi and dumped the body in the river, police said.
As the news spread, locals ransacked Ratan's house and later set it on fire. The angry mob caught Ratan while he was trying to flee. They gave Ratan a good beating and handed him over to the police.