CAT/C/COL/CO/4 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 safety and the lack of effective protection measures. The Committee is concerned that they have been placed under surveillance and have had their telephones tapped by Administrative Department for Security (DAS) agents, as have other actors in civil society such as trade unionists, non-governmental organizations and journalists (art. 2 of the Convention). The Committee urges the State party to put an immediate end to the harassment by DAS agents of human rights defenders and other civil society actors upholding human rights, and to punish those responsible for practices stigmatizing human rights defenders. The State party should ensure that effective protection is made available for human rights defenders and others whenever they have been threatened on account of their activities. Witness protection 24. The Committee is concerned about the frequent threats made against witnesses in cases involving torture and other cruel, inhuman or degrading treatment. The Committee is particularly concerned about the harassment and murders of witnesses and victims who have taken part in trials held under Act No. 975 of 2005. In spite of the protection programmes in place, the Committee considers that the State party has not fully complied with its duty to ensure the safety and integrity of witnesses and victims (art. 13 of the Convention). The Committee urges the State party to adopt effective measures to guarantee the safety and integrity of witnesses and victims and to strengthen protection programmes with additional resources. The Committee urges the State party to pay special attention to the protection and interim measures issued by the Inter-American Human Rights System and to take immediate and effective measures to ensure compliance with them. GE.10-42033 7