MONITORING PLACES OF DETENTION : A PRACTICAL GUIDE FOR NGOS 33 suffering serious abuse, should be the priority target of a programme to monitor conditions of detention. In practice, however, these are often the very persons who are the most difficult to visit. To sum up, priorities can be selected according to the following, non-exhaustive criteria: Category of persons deprived of their liberty ■ Age; ■ sex; ■ nationality or community of origin; ■ type of deprivation of liberty (see Table 1). Detaining authorities ■ Ministry of the Interior: police, security services, immigration services; ■ Ministry of Justice: criminal investigation department, prison authorities; ■ Ministry of Defence. The work of other players ■ Who? Who are the other players working in the field of persons deprived of their liberty? ■ For whom? What categories of persons deprived of their liberty are they interested in?