The purpose of this study is to investigate the actual conditions of infringement on human rights in the investigation/trial/correction stages for intellectually disabled suspects and analyze the problems of the system for the intellectually disabled suspects run by the criminal justice agencies to propose points of improvement for the legal system to protect human rights of the intellectually disabled. The study subjects of this paper include intellectually disabled suspects, intellectually disabled defendants, and intellectually disabled prisoner, and the intellectually disabled mentioned in this paper not only refers to the registered disabled, but is a concept that includes individuals that have temporary or permanent cognitive impairment due to age, abuse, accident, disease, lack of education, or other various causes, who are unable to understand the criminal justice procedures and cannot exercise their right to defense. Investigation on court decisions and in-depth interviews were used as methods of study. Comparing the distribution of charges among the total crimes that occurred in 2020 including non-intellectually disabled persons and the distribution of charges of the intellectually disabled defendants, the charges for the intellectually disabled are concentrated in sexual abuse crime and theft crime. As with preceding studies, due to the nature of the disability, while the proportion of the intellectually disabled that commit economic crimes is low, and the proportion of those that commit personal crime is high, most of the sexual crimes were minor offenses such as molestation, obscenity in public, and small amount takes up the majority of theft as well. Also, while most of the crimes resulted from the nature of intellectual disability, the ratio in which loss of mind and body or feeble mind is acknowledged for a sentence of not guilty is low. At least 80% of the intellectually disabled defendants were assigned public defenders, but they were careless, not even interviewing the defendants prior to testimony, and the judiciary's awareness of the disables was low, to the extent that 6.8% of the intellectually disabled defendants went to trial without an attorney. An analysis of the cases in which sentence for not guilty, suspension of execution, or exemption of sentence was declared revealed that either a detailed test result on the defendant's intellectual level is described. or the judge took into account the fact that the right to defense in the investigation procedures was not fully exercised.

When there are no procedures taken by the police to discern the mentally disabled prior to commencing investigation, there are many cases in which the police compulsively haul or voluntarily accompany the mentally disabled to the police station or patrol division, from the first report, investigation is fulfilled without the presence of a reliable person, and the mentally disabled who are illiterate tend to sign and seal the report as the police orders them to do so. Also, the number of investigators exclusively in charge of the intellectually disabled is absolutely insufficient, and capability of these investigators is also insufficient. The presence of a reliable person has the purpose of smooth communication in addition to mental stability of the intellectually disabled defendant, but the investigation agencies interpret this arbitrarily, that when the reliable person attempts to make an objection regarding unreasonable interrogation, he or she is restrained therefore, currently the role of the reliable person is very limited.

A majority of the intellectually disabled are assisted by public defenders due to economic difficulty, but many of these public defenders are careless, have no knowledge of intellectual disability, and only focus on the proceedings. The prosecutor and judge presumes the intellectually disabled to be guilty to proceed with prosecution and ruling. Also, the administration of court is also discriminating, as decisions or trial deadlines are only sent as s, without other methods such as phone, etc., even though the majority of the intellectually disables are illiterate.

Correction and probation do not have specialized facilities or experts that educate and discern the intellectually disabled, and particularly, the intellectually disabled cannot complete the training order, community service, etc. executed at the probation agency and are often arrested due to violation of regulation. Correctional institutes accept the severely intellectually disabled separately for living support, but the minor intellectually disabled and borderline intellectually disabled live together with non-disabled persons, experiencing violence, extortion, or receiving additional sentence due to being used for illegal action.

Rather than identifying the type of disability for intellectual disability, procedures or indicators to check whether one has trouble making decisions, communicating, and judgment are necessary. As there are many intellectually disabled persons that are not registered, as with the case in UK, when there is suspicion through the identification indicators, the necessary support such as the reliable person, should be provided. The reliable person should be allowed to monitor whether the formal procedures of the investigation are fair and appropriate by accompanying the intellectually disabled, and his or her authority to make an objection or give an opinion should be acknowledged. Regarding the function of "smoothly communicating," as the intellectually disabled do not understand their rights in the investigation process most of the time, medical aid should be permitted in delivering the duty to notify, such as right to receive assistance from an attorney, or right to remain silent. The reliable person should participate in such procedures to check whether the testimony was written appropriately and procedures that enable him or her to request correction for errors should be established. 

A systematic training curriculum regarding the support measures and right of the disabled in all jurisdiction procedures including detention facilities and probation facilities should be established, and they should be included in the regular curriculum. As with the US NCCID's "Pathways to Justice" program, measures to cooperate with non-jurisdiction domains such as the civil society with long experience and expertise or the field of the disabled are needed.