Additional District and Sessions Judge of Banka, Sanjay Kumar Singh, passed the order after finding them guilty of murdering the boy.
According to the prosecution, Krishnanand was kidnapped on December 30, 2012, for ransom and later killed. His body was subsequently recovered from a water body in Dharma hills on January 5, 2013.
The victim's family had lodged an FIR charging the three persons with the kidnapping and murder of the boy.
The convicts - Sonu Kumar, Nawal Kishore Mandal and Bhola Panjiar and the boy hailed from Nanaichak village.