CAT/C/CHL/CO/5 page 7 The State party should: (a) Adopt effective measures to improve material conditions in the prisons, reduce the current overcrowding and properly meet the basic needs of all persons deprived of their liberty; (b) Establish a national prevention mechanism that is authorized to carry out periodic visits to detention centres in order to fully implement the Optional Protocol to the Convention against Torture; (c) Establish security measures that are in keeping with respect for the dignity of persons deprived of their liberty, which entails doing away with isolation cells. Deprivation of liberty in the case of adolescents 22. The Committee takes note of the efforts that the State party has made to improve the regime governing the deprivation of liberty in the case of adolescents. Nevertheless, the Committee is concerned about some shortcomings in centres where adolescents are held, such as serious overcrowding, the failure to separate different categories of inmates and an inadequate supply of basic services. The Committee is also concerned by reports of excessive use of force and the use of isolation as a punishment in such centres (art. 16). The State party should: (a) Take the necessary steps to ensure that adolescents are deprived of their liberty only as a measure of last resort; (b) Ensure that adolescents deprived of their liberty have access to workshops and training courses and to an adequate supply of basic services, especially as regards health care. It should also ensure that adolescents deprived of their liberty are provided with proper legal aid when they need it; (c) Eliminate any possibility that disciplinary measures, especially measures amounting to isolation, might be applied without due process; (d) Take steps to combat overcrowding in these centres; (e) Ensure that the law on the criminal responsibility of adolescents requires that the treatment they receive is in accordance with international standards and principles. Indigenous peoples 23. The Committee takes note of the text of the constitutional amendment now before Congress which accords recognition to indigenous peoples. The Committee also welcomes the establishment of an ombudsman’s office for indigenous peoples specializing in criminal matters. Nevertheless, the Committee is concerned by the many reports that it has received regarding the continuing commission of abusive acts by police officers against members of indigenous