A/65/44 take place within a legal framework that recognizes the obligations imposed by the Convention. Arbitrary detentions (20) The Committee is concerned about the high incidence of arbitrary arrests, and in particular the use of preventive administrative detention by the police and mass arrests by the police and the army. The Committee notes that arrest warrants are frequently insufficiently substantiated by evidence and that arrests are used as a means of stigmatizing certain groups such as community leaders, youth, indigenous people, Afro-Colombians and peasants (art. 2 of the Convention). The Committee recommends that the State party take steps to eradicate preventive administrative detention and mass arrests, and act on the recommendations made by the Working Group on Arbitrary Detention following its mission to Colombia in 2008 (A/HRC/10/21/Add.3). Conditions in detention (21) The Committee remains concerned about conditions in detention in the light of persistent overcrowding and continuing complaints of torture and other cruel, inhuman or degrading treatment in prisons and places of temporary detention. The Committee is concerned that prolonged solitary confinement is used as a form of punishment. It has received reports of inhuman or degrading treatment in the Valledupar high- and mediumsecurity prison and the Bellavista prison in Medellín. The Committee is concerned that complaints about cases of torture and inhuman treatment tend to be dealt with through disciplinary proceedings alone, and that it has rarely been possible to carry out investigations. The Committee is also concerned about the military nature of the prisons and the scant availability of mental health services for prisoners (arts. 11 and 16 of the Convention). The State party should adopt effective measures to improve material conditions in prisons, reduce the current overcrowding and properly meet the basic needs of all persons deprived of their liberty. The use of solitary confinement should be reviewed and restricted. Complaints of torture and other cruel, inhuman or degrading treatment in prisons and places of temporary detention should be promptly and impartially investigated and brought to the attention of the criminal courts. Optional Protocol (22) The Committee takes note of the State party’s decision to reject ratification of the Optional Protocol to the Convention and its claim that this role is already performed by the human rights committees constituted by the Office of the Ombudsman and prisoners, on the grounds that the internal regulations (resolution No. 5927/2007) of the National Penitentiary and Prison Agency (INPEC) provide a mechanism to guarantee the human rights of prisoners by means of a consultative and decision-making process within the committees of each prison, in which prisoners and the offices of the Public Prosecutor and the Ombudsman participate directly. Although the Committee notes that the initiative to set up human rights committees in prisons is a positive development, it is concerned that such mechanisms are supervised by INPEC and do not constitute an independent preventive mechanism as provided for by the Optional Protocol (art. 2 of the Convention). The Committee recommends that the State party ratify the Optional Protocol to the Convention as soon as possible, the better to prevent violations of the Convention. Human rights defenders (23) The Committee reiterates its concern about the stigmatization of human rights defenders and their families, the high incidence of threats, the frequent attacks on their GE.10-44721 23