(18) While noting the measures taken by the State party to address the crucial problem of prison overcrowding, including by building new prisons and considering alternatives to detention, the Committee remains concerned about the poor detention conditions in prisons, particularly in the Loos and Toulon short-stay prisons, and in administrative holding centres. The Committee is particularly concerned about the inadequacy of internal inspections, the unsuitability and dilapidation of the buildings, and the unsatisfactory hygiene conditions. It is also concerned about the increase in violence among detainees and in the number of suicides reported to it (arts. 11 and 16). The Committee recommends that the State party should take the necessary steps to ratify the Optional Protocol to the Convention as soon as possible, and to set up a national mechanism to conduct periodic visits to places of detention in order to prevent torture and any other cruel, inhuman or degrading treatment. (19) The Committee notes the measures taken by the State party to improve living conditions in holding areas, particularly at Roissy-Charles de Gaulle airport, and to facilitate access to them by non-governmental organizations. However, it remains concerned about information it has received concerning incidents of police violence, including cruel, inhuman and degrading treatment, inside the holding areas, particularly against people of non-Western origin (arts. 11 and 16). The Committee recommends that the State party should take the necessary measures to enable the National Commission for the Monitoring of Holding Centres and Facilities and Waiting Areas to begin its work soon and to ensure that these recommendations are effectively implemented. (20) While taking note of the draft decree on solitary confinement mentioned by the State party, the Committee is concerned that the draft does not set any time limit and that no special justification is needed until two years have been spent in solitary confinement. The Committee is worried that detainees can be held under this regime for many years despite its possible harmful effects on their physical and mental state (art. 16). The Committee recommends that the State party should take the necessary measures to ensure that solitary confinement remains an exceptional measure of limited duration, in accordance with international standards. Impartial investigation (21) The Committee continues to be concerned about the system of discretionary prosecution, which gives State prosecutors the option of not prosecuting the perpetrators of acts of torture and ill-treatment in which police officers are implicated, or even of not ordering an investigation, which is clearly contrary to article 12 of the Convention (art. 12). The Committee reiterates its recommendation (A/53/44, para. 147) that, in order to comply with article 12 of the Convention in letter and in spirit, the State party should consider abrogating the system of discretionary prosecution so as to remove all doubts regarding the obligation of the competent authorities to launch impartial inquiries systematically and on their own initiative in all cases where there are reasonable grounds for believing that an act of torture has been committed in any territory under its jurisdiction, in the spirit of the recommendation of the Human Rights Committee (CCPR/C/79/Add.80, para. 15), which calls on the State party to “take appropriate measures to fully guarantee that all investigations and prosecutions are undertaken in full compliance with the provisions of articles 2, paragraphs 3, 9 and 14 of the Covenant”. 29