BOUYID v. BELGIUM JUDGMENT 21 officers abusing their power vis-à-vis persons who were completely under their control. In such cases the severity threshold should be lowered. With reference to Salman v. Turkey ([GC], no. 21986/93, ECHR 2000-VII), Denis Vasilyev v. Russia (no. 32704/04, 17 December 2009) and Valiulienė v. Lithuania (no. 33234/07, 26 March 2013), the third-party intervener pointed out that the Court considered that persons in police custody were in a vulnerable position and that Article 3 imposed a duty on States to protect the physical well-being of persons who were in such a position, and that it took account of the victim’s feeling of fear and helplessness in assessing whether the Article 3 threshold had been reached. The third-party intervener took the view that the same applied even more so to minors deprived of their liberty, given their particular vulnerability. In this context, a mere slap could have serious psychological repercussions which were incompatible with the requirements of Article 3, especially as such a slap could be taken as a threat of more severe violence in the event of refusal to cooperate, or even as a punishment. 74. The third-party intervener invited the Court to take account of the fact that in its 2006 and 2010 reports on Belgium (cited above) the CPT had recommended that the Belgian authorities remind “police officers ... that when making an arrest, the use of force must be kept to what is strictly necessary [, and that] there can never be any justification for striking apprehended persons once they have been brought under control”. 75. The third-party intervener then pointed out that in Davydov and Others v. Ukraine (nos. 17674/02 and 39081/02, § 268, 1 July 2010), the Court had held that Article 3 required States to train law-enforcement officials in such a way as to give them a high level of competence in their professional conduct, such that no one could be subjected to treatment contrary to that provision. 76. Lastly, the third-party intervener highlighted the fact that the use of violence by the police was not unusual in Belgium. Like the applicants, it referred to the statistics published by Committee P and OBSPOL. It added that the Belgian police force had been involved in several cases of police violence in recent years, and that in some police stations in the Brussels region, flat-hand slapping (in order to leave as few marks as possible) had been found to constitute virtually a routine occurrence. 2. REDRESS 77. This third-party intervener stressed that international human rights law only allowed the use of physical force by law-enforcement officials to the extent that it was necessary and proportionate to a legitimate aim. It referred to Article 10 of the International Covenant on Civil and Political Rights, General Comment No. 20 of the UN Human Rights Committee, the UN Code of Conduct for Law Enforcement Officials, the UN Basic Principles on the Use of Force and Firearms by Law Enforcement Officials,