When the North’s Korean Central News Agency reported Sunday that a North Korean defector had returned to the North by crossing the military demarcation line, the report sounded dubious at first. But as time went by, the North’s claims seemed to fit the facts.

South Korean military officials said Monday that they believed a 24-year-old man surnamed Kim, who fled here from the North in 2017, had swum to the North from the western island of Ganghwado after going through a drain under double barbed-wire fences installed to guard against infiltrators. The drain leads to a Han River estuary adjacent to the Yellow Sea.

Near the drain they found a bag they believe is Kim’s. At its closest point, Ganghwado is only about 1.3 kilometers from North Korea.

The South is obligated to protect North Koreans who swim to Ganghwado with the intention of defecting. But infiltrators and wanted criminals must not be allowed to come through undetected.

It is concerning that the South Korean military authorities hurriedly checked North Korea’s claims about the incident only after the news report came out.

According to the North’s report, the man had previously “escaped” to the South but crossed the demarcation line July 19 to return to the North. The South Korean military authorities were in the dark for about a week. If not for the North’s report, they would not even have known what happened. That means they also cannot know who may be infiltrating the South from the North.

The military demarcation line must be perfectly guarded, but it was breached easily by a North Korean defector. Kim reportedly swam to Gyodongdo, another island near Ganghwado, when he defected to the South. If a North Korean civilian managed to cross the demarcation line twice, undetected, how much easier would it be for a trained North Korean spy to infiltrate the South?

This is not the first time the line has been breached. In October 2012, a North Korean soldier crossed the border unchecked and knocked on the door of a South Korean guard post in Goseong, Gangwon Province, asking to defect. In June last year, North Koreans on a fishing boat entered the port of Samcheok, Gangwon Province, and also asked to defect. Their boat reached the pier without being detected.

Whenever the military fails to detect an illegal crossing, they vow to prevent a recurrence. However, similar incidents keep happening. The holes that make the border porous must be identified and filled.

Kim’s return to the North also exposed slack management on the part of the South Korean police, who are in charge of monitoring North Korean defectors.

The police failed to determine Kim’s whereabouts until they saw the news report from the North. They are now embroiled in controversy over signs that he planned to go back to North Korea. The police say they received no such information, but one of Kim’s acquaintances says she tipped off the police on several occasions.

Furthermore, Kim was accused of raping another North Korean defector, yet the police did little about it even after receiving DNA evidence from the National Forensic Service on July 4. The police eventually requested an arrest warrant and banned Kim from leaving the country -- but only after he had gone back to the North.

If the military and the police had their operations in order, this incident might not have happened.

North Korea said it was taking “maximum” emergency precautions against the coronavirus after a defector returned with coronavirus symptoms. This claim is hard to verify. South Korean health officials said Kim was not registered as a COVID-19 patient, nor was there any evidence that he ever came into contact with anyone who’d tested positive.

If the coronavirus has spread across North Korea, South Korea may offer humanitarian help. But any attempt by the North to shift responsibility to the South must be blocked.