90. Mr Assenov alleged that the events of 19 September 1992 had given rise to violations of Article 3 of the Convention, which states: “No one shall be subjected to torture or to inhuman or degrading treatment or punishment.” He contended that this Article had been breached on two separate grounds. First, he asked the Court itself to examine the medical evidence and witness statements which, he alleged, demonstrated that he had been severely beaten by police officers. Secondly, joined by the interveners (see paragraph 5 above), he asked the Court to declare that wherever there were reasonable grounds to believe that an act of torture or inhuman or degrading treatment or punishment had been committed, the failure of the competent domestic authorities to carry out a prompt and impartial investigation in itself constituted a violation of Article 3. 91. The Government pointed out that the applicant’s medical certificate was unreliable because it had been issued two days after the incident in question. In any case, the injuries which it described, and the absence of any certificate relating to Mr Ivanov, were consistent with the witnesses’ accounts of the father having beaten his son with a thin strip of wood. 92. In assessing the evidence before it, the Commission had regard to the principle that where an individual alleges to have been injured by ill-treatment in custody, the Government are under an obligation to provide a complete and sufficient explanation as to how the injuries were caused (see the Ribitsch v. Austria judgment of 4 December 1995, Series A no. 336, pp. 25-26, § 34 and the above-mentioned Aksoy judgment, p. 2278, § 61). It accepted, inter alia, that a quarrel had erupted at the bus station between the police officers and Mr Ivanov, that the latter had hit his son with a plywood strip in an effort to show that he would punish the boy himself and that both applicants were then detained at the police station for approximately two hours. However, more than four and a half years after these events, and owing to the lack of a sufficiently independent and timely investigation by the domestic authorities, the Commission was not able to establish which version of events was the more credible. It did not, therefore, find any violation of Article 3. 93. Article 3, as the Court has observed on many occasions, enshrines one of the fundamental values of democratic society. Even in the most difficult of circumstances, such as the fight against terrorism or crime, the Convention prohibits in absolute terms torture or inhuman or degrading treatment or punishment. Unlike most of the substantive clauses of the Convention and of Protocols Nos. 1 and 4, Article 3 makes no provision for exceptions and no derogation from it is permissible under Article 15 even in the event of a public emergency threatening the life of the nation (see the above-mentioned Aksoy judgment, p. 2278, § 62). 94. The Court recalls that ill-treatment must attain a minimum level of severity if it is to fall within the scope of Article 3. The assessment of this minimum is relative: it depends on all the circumstances of the case, such as the duration of the treatment, its physical and/or mental effects and, in some cases, the sex, age and state of health of the victim. In respect of a person deprived of his liberty, recourse to physical force which has not been made strictly necessary by his own conduct diminishes human dignity and is in principle an infringement of the right set forth in