The father put his five-year old son to sleep on his lap after dinner on Sunday. He bought the boy outside the house around midnight and met his brother.
The duo then killed the boy, cut off his ears and genital and hung the body from a tree after lodging two knives in his belly. The knives had two names written on the grips.
This is how the police described the murder of Tuhin Hasan in a latest update, adding that the boy's father and uncle murdered him to frame their rivals.
Mijanur Rahman, Sunamganj's Additional Superintendent of Police, briefed the media on Tuesday afternoon, saying Tuhin's father Abdul Basir and uncle Abdul Mosobbir murdered the child.
"We are investigating the matter and optimistic about unearthing a clear motive soon," Mijanur told reporters.
The duo confessed their crime before a court earlier in the day. Police then took the brothers and their neighbour Jamshed Ali on a three-day remand.
Police on Monday morning found the boy's body in Kejaura area of Derai Upzila in Sunamganj.
The gruesome killing rocked the country to its core and drew huge criticism at various social media platforms. Police on suspicion detained seven people including the boy's family members and neighbours.
Later in the afternoon, police told the media that two or three family members might be involved in Tuhin's murder.
On Tuesday morning, Tuhin's mother Monira Begum filed a case with Derai Police Station.
According to locals, Tuhin's father has a longstanding rivalry with a former local union parishad member.