The International Standard of Intellectual Disability and the Imposition of the Death Penalty


The author, Jean-Paul Ong, was the AHRCentre- Reprieve student intern for semester 1, 2015. Read more about the internship here.


The laws of many countries address the situation of persons who have a mental illness or intellectual disability when they are caught up in the criminal justice system. The issues that arise include whether such persons bear criminal responsibility for particular acts at all, whether they were capable of satisfying the required mental state (mens rea) to be held liable for a crime, whether they are competent or fit to stand trial, and whether their mental illness or intellectual disability is relevant to the nature of the sentence imposed or mitigation of sentence or to executive clemency. All these issues arise with particular force in capital cases.

Whether a person who has a mental disorder, be that at the time of the alleged commission of an offence, at the time of trial and sentencing, or at the time of the carrying out of a death sentence, or who suffers from intellectual disability, should be tried, convicted or executed for a capital offence, raises fundamental questions of justice, the purposes of the criminal justice system, and the relationship between the criminal justice system and medical science. Most, if not all States, including capital punishment States, have legislative or other rules that address the way in which the rules of criminal liability and punishment apply to those with mental illness or intellectual disability at different stages of the criminal justice process. These protections are sometimes based on outmoded understandings of the nature of mental disorders or intellectual disability. There are documented cases in which, despite the existence of constitutional or legislative guarantees, persons with claimed or demonstrated intellectual disability, been sentenced to death and executed in circumstances which violate fundamental human rights, either because they were not provided with appropriate medical examinations or because clear evidence was not taken into account in sentencing and execution decisions.

In 1989, the United Nations Economic and Social Council (ECOSOC) adopted Safeguards guaranteeing protection of the rights of those facing the death penalty and explicitly called on member States to consider the mental health of accused and convicted persons and recommended that member States eliminate the death penalty ‘for persons suffering from mental retardation or extremely limited mental competence, whether at the stage of sentence or execution’.

However, a critical issue is the lack of an international legal standard defining intellectual disability. Definitions of intellectual disability vary widely from country to country, with some conflating the term with mental illness, and others completely excluding intellectual disability from their definitions.

As of 2015, there are still ninety-two countries that still allow the death penalty. Many of these countries provide exemptions from criminal liability or limit the imposition of the death sentence on persons with mental illness or intellectual disability. They often describe these persons to be ‘insane’ or ‘of unsound mind’, a description that may cover both persons with mental illness and persons with intellectual disability.

While recognising that these two categories of persons are often dealt with under the same legal provision, mental illness and intellectual disability need to be analysed as two distinct conditions. There is much debate about the scope of these terms and whether they encompass all the relevant physical or mental conditions that may be relevant to criminal liability and punishment. The term intellectual disability is widely understood to describe the condition of an individual who is of low intelligence and is significantly limited in general intellectual functions.

Endorsed by the US Supreme Court in Atkins v Virginia, the American Association on Intellectual and Developmental Disabilities (AAIDD) defines intellectual disability as a:

substantial limitation in present functioning and manifesting before age 18. It is characterized by significantly sub-average intellectual functioning, existing concurrently with related limitations in two or more of the following applicable adaptive skill areas: communication, self-care, home living, social skills, community use, self-direction, health and safety, functional academics, leisure, and work. 

Generally, persons with intellectual disability have a lesser capacity to understand the meaning and consequences of their actions and are less likely to be deterred by threats of punishment; they are more vulnerable when they fall into the hands of the criminal justice system, likely to be more suggestible, more ready to seek to please by confessing, less knowledgeable about their rights without legal assistance, less adept at negotiating pleas, and therefore more susceptible to being wrongly convicted.


Despite the existence of constitutional or legislative guarantees, the sentencing to death of persons with intellectual disability is still an ongoing issue. The failure to provide such defendants with appropriate medical examinations or to take into account clear evidence in sentencing and execution decisions involves violations of fundamental human rights. The problem lies partly with capital punishment jurisdictions’ definition of intellectual disability and in particular the diagnosis of these conditions, with some countries adopting definitions that are so stringent that even the most intellectually disabled are considered legally competent for the purposes of the criminal proceedings.