HWASEONG, South Korea, Jan. 13 (Yonhap) -- A 19-year-old marine corporal surnamed Kim was sentenced to death by a military court on Friday for killing four fellow marines in a shooting rampage on Ganghwa Island, west of Seoul, last July.

A marine private found guilty of assisting Kim in the July 4 rampage was also sentenced to 20 years imprisonment.

The Marine Corps court said heavy punishment was inevitable for Kim and the private, identified only as Jung, considering the circumstances of their crimes.

Military investigators concluded that Kim, who was found to be mentally unstable at the time of the shooting, was angered by alleged bullying and beatings by his colleagues.

Kim was arrested after unsuccessfully trying to kill himself with a grenade.

Following the incident, the defense ministry ordered all military commanders to inspect their standards of discipline for any irregularities.