CRC/C/GC/24 77. Recognizing the harm caused to children and adolescents by deprivation of liberty, and its negative effects on their prospects for successful reintegration, the Committee recommends that States parties set a maximum penalty for children accused of crimes that reflects the principle of the “shortest appropriate period of time” (Convention on the Rights of the Child, art. 37 (b)). 78. Mandatory minimum sentences are incompatible with the child justice principle of proportionality and with the requirement that detention is to be a measure of last resort and for the shortest appropriate period of time. Courts sentencing children should start with a clean slate; even discretionary minimum sentence regimes impede proper application of international standards. Prohibition of the death penalty 79. Article 37 (a) of the Convention reflects the customary international law prohibition of the imposition of the death penalty for a crime committed by a person who is under 18 years of age. A few States parties assume that the rule prohibits only the execution of persons who are below the age of 18 years at the time of execution. Other States defer the execution until the age of 18. The Committee reiterates that the explicit and decisive criterion is the age at the time of the commission of the offence. If there is no reliable and conclusive proof that the person was below the age of 18 at the time the crime was committed, he or she should have the benefit of the doubt and the death penalty cannot be imposed. 80. The Committee calls upon the few States parties that have not yet abolished the imposition of the death penalty for all offences committed by persons below the age of 18 years to do so urgently and without exceptions. Any death penalty imposed on a person who was below the age of 18 at the time of the commission of the offence should be commuted to a sanction that is in full conformity with Convention. No life imprisonment without parole 81. No child who was below the age of 18 at the time he or she committed an offence should be sentenced to life imprisonment without the possibility of release or parole. The period to be served before consideration of parole should be substantially shorter than that for adults and should be realistic, and the possibility of parole should be regularly reconsidered. The Committee reminds States parties that sentence children to life imprisonment with the possibility of release or parole that in applying this sanction they should strive for the realization of the aims of article 40 (1) of the Convention. This means, inter alia, that a child sentenced to life imprisonment should receive education, treatment and care aiming at his or her release, reintegration and ability to assume a constructive role in society. This also requires a regular review of the child’s development and progress in order to decide on his or her possible release. Life imprisonment makes it very difficult, if not impossible, to achieve the aims of reintegration. The Committee notes the 2015 report in which the Special Rapporteur on torture and other cruel, inhuman or degrading treatment or punishment finds that life imprisonment and lengthy sentences, such as consecutive sentencing, are grossly disproportionate and therefore cruel, inhuman or degrading when imposed on a child (A/HRC/28/68, para. 74). The Committee strongly recommends that States parties abolish all forms of life imprisonment, including indeterminate sentences, for all offences committed by persons who were below the age of 18 at the time of commission of the offence. F. Deprivation of liberty, including pretrial detention and post-trial incarceration 82. Article 37 of the Convention contains important principles for the use of deprivation of liberty, the procedural rights of every child deprived of liberty and provisions concerning the treatment of and conditions for children deprived of their liberty. The Committee draws the attention of States parties to the 2018 report of the Special Rapporteur on the right of everyone to the enjoyment of the highest attainable standard of physical and mental health, in which the Special Rapporteur noted that the scale and magnitude of children’s suffering in 13