The convicts are Bibek Mandal, Sougat Roy and Arunav Roy. All of them were tried in absentia.
Crime Prevention Tribunal of Khulna Judge Md Saifuzzaman Hero handed down the verdict.
According to the prosecution, police recovered the body of Gobinda Sana from a river on November 22, 2015.
Krishnapodo Sana, younger brother of the victim, filed a case in this connection.
Police suspected that Gobinda was killed by the convicts between November 19-November 21.
On June 16, 2016, police submitted a chargesheet against three people.
The trial proceeding of the case started on July 5, 2018 with the charge framing.