The suicide of a serial killer on death row, upon which the South Korean justice ministry was accused of lax supervision of prisoners, has also brought back the debate on capital punishment.

Forty-year-old Jeong Nam-gyu, one of the most notorious murderers sent to death row, was found at 6:35am Saturday (November 21). He had hanged himself using a rope made of a plastic trash bag in his solitary cell, according to officials.

Jeong was sentenced to death in 2007 for killing 13 and injuring seven from 2004-2006.

He was immediately sent to the hospital but died 20 hours later, said officials. His was the second death row suicide since a killer surnamed Kim hanged himself in his cell in February 2007.

Jeong left notes hinting at the mental pressure he felt from the possibility of being executed. "They have no plans to abolish the death sentence. Life is but a floating cloud," he wrote.

A total of 61 prisoners, including Jeong, were on death row, but no prisoners have been executed in Korea since December 1997. Amnesty International has since classified the country as "abolitionist in practice".

However, the public has recently come to call for harsher punishment on felons such as serial killers and sex offenders, especially following the shocking crimes by serial killer Kang Ho-soon or child rapist Cho Doo-soon.

Though some religious circles and human rights groups took Jeong's case as an example to once again demand that capital punishment be abolished, the ministry is not planning to accept the claim, according to officials.

The prison in which Jeong died was held responsible for leaving Jeong unattended for sufficient time to kill himself.

Korea has the highest rate of prison suicide in the OECD. An average of 100 prisoners over 47 prisons attempt suicide each year and 72 have succeeded so far since 2005. More than 30 percent of them were murderers, many of whom had been given the death sentence.

The prison was also criticised for leaving a prisoner with a means of committing suicide.

A total of 836 prisoners have been caught since 2004 with forbidden items, such as cigarettes, cash, checks, mobile phones and drugs. The finding raises the possibility that items that could be used in suicide may also be smuggled in.

"It is practically impossible to strip a prisoner of all daily necessity goods, such as trash bags," said a ministry official.

Critics say that the prison should keep a keener eye on its inmates, especially those on death row, who may take more extreme actions, having little to lose.

Some point out that no CCTV cameras were installed. The law was revised last year to limit the use of CCTV strictly to mentally unstable prisoners who require special surveillance.