Nagaenthran, who was convicted of trafficking in 42.72gm of diamorphine (heroin) in 2011, is expected to be executed on Nov 10.

In a statement, ADPAN said the Singaporean authorities should not proceed with the execution as Nagaenthran suffers from a mental disability.

“His IQ has been assessed to be 69, a level that is internationally recognised as an intellectual disability. During his trial, his defence raised evidence that he suffers from intellectual disabilities that impair his rationality and ability to assess risk.

“The defence was dismissed despite psychiatric assessment highlighting his inability to make judgments, decision making, impulse control, and ability to assess future consequences. The assessment notes that his condition was influenced by severe alcohol use disorder, severe attention deficit hyperactivity disorder, and borderline intellectual functioning,” it said.

ADPAN claimed that Singapore had violated international laws that restrict the application of the death penalty to the “most serious crime”, which exclude drug offences, and of sentencing a mentally disabled person to death.

“Singapore’s insistence to convict, sentence and execute a person suffering from intellectual disabilities violates the country’s obligations under the United Nations Convention on the Rights of Persons with Disabilities, which Singapore ratified in 2013.

“ADPAN calls for the Singapore government to commute Nagaenthran’s death sentence and ensure that he is given the appropriate mental health assessment and care in line with the convention,” it said.

Yesterday, another rights group, Lawyers for Liberty, urged the government to make representations to the Singapore authorities to spare Nagaenthran from the gallows.

LFL adviser N Surendran said the government could lodge a report with the International Court of Justice (ICJ).