A military court sentenced an Army sergeant to 45 years behind bars on Thursday for abusing and beating his junior comrade to death.

The sergeant, identified only by his surname Lee, was convicted of killing the 23-year-old Army private first class, surnamed Yoon, after brutally abusing him at their frontline unit on the east coast. 

In April, Yoon died after allegedly being hit in his chest by six of his colleagues while eating snacks. The assault caused a piece of food to obstruct his airway, leading him to die of asphyxiation, the Army said, adding that his death also resulted from damage to his skeletal muscle caused by repeated assaults for about a month.

The Army's General Military Court in Yongin, just south of the capital city of Seoul, also ruled that another sergeant, surnamed Ha, should face 30 years in prison; two corporals 25 years behind bars; and two other soldiers, a staff sergeant and a private first class, 15 years and three months with six months of probation, respectively. 

"It is inevitable to hand them down severe punishments as what Lee had done constitutes as homicide," the judge said in a verdict. 

Excluding the staff sergeant's case, the court ruling was more lenient than what military prosecutors had sought: the death penalty for Lee as well as life in prison for Ha and the two corporals for their alleged role in Yoon's death. The military prosecutors also demanded the staff sergeant and the private first class be sentenced to 10 years and six months in prison,

respectively.    

The prosecutors first charged them with involuntary manslaughter, but later reversed it to bring murder charges amid revelations that the victim had long suffered severe assaults and abusive treatment by his colleagues. 

The case, which was brought to light belatedly in a media report, is among a series of incidents that have laid bare the chronic problem of bullying in the barracks and a rigid military culture. 

In June, an Army sergeant who had been bullied by his comrades went on a shooting spree at a border outpost on the east coast, killing five soldiers and wounding seven others.

All able-bodied South Korean men are subject to compulsory military service for about two years in a country facing North Korea across the heavily fortified border. (Yonhap)