Additional District and Sessions Court Judge Md Fazle Elami Bhuiyan gave the verdict on Thursday.
Two brothers were among the convicts handed down the death sentence by the court for the 2004 murder. The two brothers and another convict were present in the court when their sentences were read out.
Those convicted were Zaman Sarkar, 42, Md Shakil Bhuiyan, 42, Md Iqbal Hossain Bhuiyan, 40 and Abu Sayem, 40.
Abu Sayem is absconding.
Zaman Sarkar of Pubail's Hazibarhi Tek area had proposed the sister of the murder victim Mamun, who was an eighth grade student at Govt Bhadun High School, said court inspector Md Rabiul Islam quoting the case details.
"But Mamun's family refused the proposal. Mamun went missing after Zaman called him to his home on Aug 10."
The 15-year-old boy's body was found in a decomposing state inside a septic tank in a house in the neighbourhood three days after he had gone missing. His hands and legs were tied and both his eyes had been gouged out. There was also a piece of cloth tied around his neck.
Source: Bangladesh's First Internet Newspaper