The 24-year-old North Korean defector who recently returned to the North was detected multiple times by the South Korean military before reaching his destination, an internal investigation revealed Friday.

South Korea’s Joint Chiefs of Staff said the defector, identified only by the surname Kim, took a cab to Ganghwado, an island west of Incheon bordering the North, crawled through a drainpipe and cut through rusty barbed-wire fences.

It took Kim about two hours to complete the journey, from the time he set foot on Ganghwado at 2:18 a.m. to the time he reached the North at 4:14 a.m.

The South Korean military admitted to lax security, as Kim should have been checked by a guard when he got out of the cab, saying the fences at the end of the drainpipe leading to the Han River estuary should have stopped him.

“The guard who spotted the cab that night thought one of the villagers was nearby, but he should have checked up on the individual,” a military official said. “We had not scanned the fences, which we should have done every day.”

The military said plastic and other waste in the river had prevented its surveillance cameras from tracking Kim in real time as he swam. The escape route was recreated after the military analyzed what was left of the footage. The original footage was not entirely backed up because of an equipment malfunction.

Two top commanders -- one at the Marine Corps and the other at the Capital Corps -- received warnings over the breach, but their superior, the ground operations commander, suffered no repercussions. A Marine Corps major general in charge of a division in the area where Kim defected was relieved of duty.

By Choi Si-young (siyoungchoi@heraldcorp.com)