The Marine Corps on Wednesday arrested a private for allegedly aiding the recent shooting spree on a seaside unit, a military official said.

According to the official, the private, whose name was withheld, is accused of failing to stop the shooter, a corporal named Kim, when Kim was taking out ammunition from a locker to load a rifle.

Kim opened fire inside the barracks on the Ganghwa Island unit west of Seoul on Monday, killing four and injuring another. Kim himself was injured after he detonated a hand grenade inside a warehouse in an apparent suicide attempt.

"The military police are trying to determine whether the private had plotted the shooting with Kim prior to the event, or whether the private was aware of the plan beforehand," the official said. "I understand that Kim on Tuesday identified the private as someone who helped him."

Kim, 19, admitted to investigators on Tuesday that he had been ostracized by both his superiors and juniors on the 30-deep Marine unit. A report claimed Kim had anxiety and personality disorders and showed signs of schizophrenia before joining the unit last September.

Later Wednesday, the Marine Corps held a joint funeral for the four victims. Lt. Gen. Yoo Nak-jun, the commander of the Marine Corps, apologized to the surviving families for his failure to protect the Marines.

"We will try to make sure our soldiers never again hurt each other," Yoo said in his eulogy. "The sacrifice and strong military spirit of our fallen comrades will stay in our hearts forever."

GySgt. Lee Seung-hoon, Sgt. Lee Seung-ryeol, Sgt. Park Chi-hyun and Cpl. Kwon Seung-hyuk were each posthumously promoted. They will be laid to rest at the Daejeon National Cemetery, south of Seoul, in a separate ceremony later Wednesday.

(Yonhap News)