Judge ABM Sajedur Rahman of Dhaka's Third Speedy Trial Tribunal pronounced the verdict over the 2012 murder on Sunday.
The court also fined the six, who got life sentences, Tk 20,000 each , failing to pay which would get them an additional year of rigorous imprisonment.
On Mar 6, 2012, retired army person Nazmul Huda was beaten and hacked at Dhamrai. He died at a local hospital later.