District and Sessions Judge Akhilesh Kumar Jain held the four persons guilty under 302 of IPC and sentenced them to life imprisonment.
The court also slapped a fine of Rs 5,000 each on Mukesh Kumar, Bablu Sah, Vijay Sah and Jitendra Mishra.
The first three hail from Ratanpura village of Bhagwanpur police station area while Mishra is from Imadpur village of the same police station of Vaishali district.
The son of Kedar Sah was killed in Ratanpura village in September 1998 by the convicted persons. The body of the deceased was recovered from Imadpur village.