6:21 a.m. Police had taken custody of the suspect, who is identified only by his surname Kim, the previous day on charges of murder and abandoning a body.

According to police, Kim appeared to have strangled himself with his garment straps in the bathroom. He was taken to a nearby hospital where he was pronounced dead later.

The CCTV footage taken around the jail showed a police officer, who was on duty, dozing off as Kim was committing suicide.

The police officer woke up around 6:21 a.m., about 1 hour and 20 minutes after the suspect entered the bathroom, and found him on the floor inside it, according to the CCTV footage.

Police officers responsible for the jail worked in four-hour shifts, violating an in-house rule that they should work in a shift of two hours, investigative sources said.

The police authorities, who have relieved the officers of their duties while an internal investigation is ongoing, plan to take punitive action against them after further looking into the incident.

His arrest came after the man, surnamed Chang, was found dead at a construction site on the town's reclaimed land on Dec. 18. A worker, who was digging at the site, found Chang strangled with a cord wrapped around his neck.

A subsequent investigation by police showed that a vehicle driven by Kim had been spotted around the site and Kim went into hiding. Police were able to track him to a hideout in the southwestern city of Gwangju.

Kim was helping Chang open a cellphone account and take out loans, police said.

The police had been questioning Kim, suspecting he was behind the murder, but Kim denied the allegation. (Yonhap)