Justice Manas Basu of the Fast Track court, Rampurhat convicted the 20 in the murder of Dost Mohammed on October 5, 2002 at a tea stall.
One of the 20 was sent to the Juvenile Justice Board for being a minor.
According to the prosecution, Mohammad was attacked while sitting in a tea-stall with his brother Bajle Rehman at Kamarkhur village under Murarai police station area.
While Bajle managed to escape, the convicts hurled bombs at the victim and injured him with sharp weapon.
He was taken to Murarai hospital in very critical condition where the doctors declared him dead.
Altogether 22 persons had been arrested in the case and two acquitted later.
