A sex offender was arrested Friday in Seoul for sexually abusing children at a hospital.

The man was wearing an electronic tag at the time of the offence, raising questions over the effectiveness of monitoring devices.

Police arrested the 48-year-old man, only identified by his surname Lim, on charges of sexually molesting children who were being treated at the hospital, Seoul Metropolitan Police Agency said Friday.

Lim was apprehended Tuesday evening for taking two children’s clothes off and touching them at a children’s hospital in Seoul.

Police are looking into whether Lim committed similar crimes elsewhere.

The case raises concerns over the effectiveness of the monitoring system, as authorities failed to prevent the crime despite the sex offender was wearing one and under surveillance.

The government introduced the system in 2008 to deter sex criminals from reoffending, despite the controversy that the system might infringe on the convicts’ human rights.

Under the system, sex offenders are required to wear an electronic tag for up to 30 years after they are released from prison.

If they try to destroy it or move outside a permitted area, probation officers are automatically notified.

But the monitoring system appears to be ineffective in preventing repeat offenses, with the number of convicts destroying their electronic tags and committing sexual crimes growing in recent years.

According to the Ministry of Justice, the number of sex offenders who reoffended while tagged rose from three in 2010 to 30 in 2013.

In March, a 20-something man was captured in Daegu after committing sex crimes on three occasions with his electronic device on.

A 30-something sex criminal cut off his anklet and escaped last month, though he was later apprehended in Seoul by the police.

An official from Ministry of Justice admitted that it was difficult to monitor tagged offenders round the clock, especially late at night, due to staff shortages.

“The Justice Ministry will step up monitoring and instruct those wearing the device to return home before midnight,” the official said.

By Ock Hyun-ju  (laeticia.ock@heraldcorp.com)