light of the provisions of the Convention and its relevant practice (for a relevant summary, see Estamirov and Others v. Russia, No. 60272/00, §§ 73 - 74, 12 October 2006).
122. The Court observes that the applicants complained to the law-enforcement authorities shortly after the disappearance of Kazbek Vakhayev and that an investigation has been pending since 18 October 2000. The applicant and the Government dispute the effectiveness of this investigation.
123. The Court considers that the Government's preliminary objection raises issues concerning the effectiveness of the criminal investigation which are closely linked to the merits of the applicants' complaints. Thus, it considers that these matters fall to be examined below under the substantive provisions of the Convention.
II. Alleged violation of Article 2 of the Convention
124. The applicants complained under Article 2 of the Convention that their family member had disappeared after having been detained by Russian servicemen and that the domestic authorities had failed to carry out an effective investigation into the matter. Article 2 provides:
"1. Everyone's right to life shall be protected by law. No one shall be deprived of his life intentionally save in the execution of a sentence of a court following his conviction of a crime for which this penalty is provided by law.
2. Deprivation of life shall not be regarded as inflicted in contravention of this article when it results from the use of force which is no more than absolutely necessary:
(a) in defence of any person from unlawful violence;
(b) in order to effect a lawful arrest or to prevent the escape of a person lawfully detained;
(c) in action lawfully taken for the purpose of quelling a riot or insurrection."
A. Alleged violation of Yusup Satabayev's right to life
1. Arguments of the parties
125. The applicants argued that it was beyond reasonable doubt that Kazbek Vakhayev had been killed by representatives of the federal forces. He had disappeared in the hands of the federal forces and the authorities had failed to provide any explanation as to his subsequent fate.
126. The Government submitted that the circumstances of Kazbek Vakhayev's disappearance were under investigation. The information about his death had not been confirmed. Nor had it been established that any State agents had violated his right to life.
2. The Court's assessment
(a) General principles
127. The Court reiterates that, in the light of the importance of the protection afforded by Article 2, it must subject deprivations of life to the most careful scrutiny, taking into consideration not only the actions of State agents but also all the surrounding circumstances. Detained persons are in a vulnerable position and the obligation on the authorities to account for the treatment of a detained individual is particularly stringent where that individual dies or disappears thereafter (see, among other authorities, Orhan v. Turkey, No. 25656/94, § 326, 18 June 2002, and the authorities cited therein). Where the events in issue lie wholly, or in large part, within the exclusive knowledge of the authorities, as in the case of persons within their control in detention, strong presumptions of fact will arise in respect of injuries and death occurring during that detention. Indeed, the burden of proof may be regarded as resting on the authorities to provide a satisfactory and convincing explanation (see Salman v. Turkey [GC], No. 21986/93, § 100, ECHR 2000-VII, and {Cakici} v. Turkey [GC], No. 23657/94, § 85, ECHR 1999-IV).
(b) Establishment of the facts
128. The Court observes that it has developed a number of general principles relating to the establishment of facts in
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