N Surendran, the Malaysian lawyer for Nagaenthran and his family, said this morning’s decision was a violation of Singapore’s treaty obligations under the convention.

“It’s a revolting (and) disgusting decision because the Singapore courts have essentially said that it’s all right to execute a mentally disabled person,” he told FMT.

“No civilised country or person can accept this. The court has obediently echoed what the Singapore government has been saying on this case since last year.”

Nagaenthran, 32, was sentenced to death in November 2010 for trafficking 42.72gm of heroin into Singapore in 2009.

He was scheduled to be hanged in November last year but managed to get it postponed following an 11th-hour challenge at the Court of Appeal on the grounds that he is intellectually disabled.

His mental capability diagnosis is said to have shown that he has an IQ of 69 which translates into being mentally impaired.

His case had led to Prime Minister Ismail Sabri Yaakob urging Singapore to commute his death sentence. Human rights activists and British billionaire Richard Branson have also voiced out against the sentence.

Surendran, who is also the adviser to rights group Lawyers for Liberty, urged the Malaysian government to take Singapore to the International Court of Justice over today’s court decision.