The South Korean military failed to notice a North Korean man who crossed into the South along the eastern shore last week eight out of ten times that he was caught on military surveillance.

According to the findings of an investigation by the Joint Chiefs of Staff(JCS) on Tuesday, the man is believed to have swum through the East Sea overnight wearing a hard-hat diving suit.

After reaching the shore near an observatory in the South at around 1:05 a.m. on February 16, the man passed through a drainage conduit beneath barbed wire fences set up along the shore.

He appeared on coastal surveillance cameras five times between 1:05 and 1:38 a.m. and the system rang an alarm twice, however, guards missed it. The man was seen three more times on ground fence cameras between 4:12 and 4:14 a.m., but no alarm went off.

It was not until he was detected twice between 4:16 and 4:18 a.m. near the Civilian Control Line that soldiers reported in, albeit 31 minutes later. After a three-hour manhunt, the man was taken into custody at around 7:27 a.m.

The military was also unaware of the drainage conduit, despite the Defense Ministry's order last July for all coastal guards to inspect barriers inside such tunnels after a North Korean defector escaped to the North through one along the western border.

In the wake of a recent series of security lapses, the JCS has vowed to tighten the military's discipline and supplement the surveillance system along the border.