Lance Corporal Hillary Joel was said to have carried out the murder during a cordon and search operation by the army in Damboa Local Government Area of Borno State.
He reportedly set the suspect ablaze, leading his death.
Four other soldiers were convicted for human rights-related offences ranging from assault, aiding and abetting murder and also unlawful possession of ammunition.
President of the General Court Martial, Brigadier-General Olusegun Adeniyi, says all sentences are subject to confirmation from the confirming authorities.
Adeniyi also asked the court to release the de-ranked soldiers who are to resume duties wearing their old tanks pending confirmation from the confirming authorities.
Private Chima Daniel was sentenced to 15 years’ imprisonment for his role in the torture and application of pepper on a 13-year-old minor, who later died, in a bid to make the victim confess to stealing a phone.
His accomplice, Corporal Audu Aliyu, was de-ranked to a private.
Both soldiers had also flogged two other minors aged 10 and 12 along with the 13-year-old.
The Court Martial also stripped Sergeant Balanga Samuel of his rank for desertion and miscellaneous offences related to the property of the Nigerian Army, describing his action as “cowardly, unprofessional and unprofessional.”
Balanga reportedly abandoned his unit in Kareto when his unit came under attack losing ammunition in his possession in the process.
The court also slammed five years and two years’ imprisonment to run concurrently on trooper Sunday Ogwuche who was found guilty of unlawful possession of ammunition while on welfare pass to Benue state.
The ammunition was discovered in his possession after a search was declared following the theft a mobile phone belonging to another soldier.
The mobile phone was equally found in his possession.