CRC/C/GC/24 45. Only if these measures prove unsuccessful, the child may be subjected to a comprehensive assessment of the child’s physical and psychological development, conducted by specialist paediatricians or other professionals who are skilled in combining different aspects of development. Such assessments should be carried out in a prompt, child- and gender-sensitive, gender-sensitive and culturally appropriate manner, including interviews of children and, as appropriate, accompanying adults, in a language the child understands. States should refrain from using medical methods based on, inter alia, bone and dental exam analysis, which may be inaccurate, with wide margins of error, and can also be traumatic and lead to unnecessary legal processes. In the case of inconclusive evidence, the child shall have the benefit of the doubt. Continuation of the juvenile justice measures after criminal majority 46. When a child in conflict with the law is the object of a measure of probation, education or curative treatment, or stays in a placement or is detained in a centre for children in conflict with the law, reaching 18 years does not mean the end of the juvenile justice specialised measures. The Committee recommends to States parties to ensure that these young persons can continue the completion of the programme or sentence in conditions suited to their age, maturity and needs and are not sent to centres for adults. Offences committed before and after 18 years and offences committed with adults 47. In cases where a young offender commits several offences, some occurring before and some after the age of 18 years, States parties should consider providing for procedural rules which allow the juvenile justice system to be applied in respect of all the offences when there are reasonable grounds to consider the author of these offences as being able to benefit from the specialized regime of the juvenile justice system. 48. In cases where a child commits an offence together with an adult or a group of adults, the proceedings and provisions of the specialized regime of the juvenile justice system applies to the child, whatever the conditions reserved for adults. D. The guarantees for a fair trial 49. Art. 40 (2) of CRC contains an important list of rights and guarantees to ensure that every child in conflict with the law receives fair treatment and trial. Most of these guarantees can also be found in article 14 of the International Covenant on Civil and Political Rights (ICCPR). However, the implementation of these guarantees for children requires specific aspects. The Committee wishes to emphasize the importance of the quality of the persons involved in the administration of juvenile justice for the implementation of the guarantees. Continuous and systematic training of professionals (police officers, prosecutors, legal and other representatives of the child, judges, probation officers, social workers, psychologists and others) is crucial. These professionals should be able to work in interdisciplinary teams, be well informed about the child’s, and particularly about the adolescent’s physical, psychological, mental and social development, as well as about the special needs of the most vulnerable children (see paragraphs xx-xx above). 50. Since girls in the juvenile justice system may be easily overlooked because they are a minority of child offenders, special attention should be paid to the particular needs of girls, e.g. in relation to prior abuse, special health, including psychological and mental health needs. 51. All the guarantees recognized in article 40 (2) of CRC are minimum standards, meaning that States parties can and should try to establish and observe higher standards. No retroactive juvenile justice (art. 40 (2) (a)) 52. Art. 40 (2) (a) of the Convention (see also article 15 of ICCPR) affirms that no one shall be held guilty of any criminal offence on account of any act or omission which did not constitute a criminal offence, under national or international law, at the time it was committed. This is also applicable to children meaning that no child can be charged with or 11