Additional District Judge -III Ravishankar Sinha also imposed Rs 15,000 fine on each of the five convicted - Raghvendra Narayan Singh, Vijay Singh, Vipin Kumar alias W Yadav, Nishikant Yadav alias Nishi Yadav, Ramnarayan alias Rama Yadav - and ordered the money be given to the widow.
On January 9, the judge convicted the five persons under Sections 302 (Murder), 34 (Acts done by several persons in furtherance of common intention) of IPC and Section 27 of the Arms Act in the high profile murder case.
Butan, who was the Purnia district President of Samata Party, was murdered allegedly due to political rivalry with Dilip Yadav, a RJD strongman and former Dhamdaha MLA who was among the eight named accused in the FIR.
The court, however, acquitted Yadav and two others - Manoj Yadav and Vikram Yadav alias Sanjay Yadav - for lack of evidence.
Bihar police had initially probed the murder case before CBI took over and charge-sheeted the accused in 2008. The agency produced 50 witnesses during trial.