control of interferences by the executive is an essential feature of the guarantee embodied in Article 5 para. 3, which is intended to minimise the risk of arbitrariness and to secure the rule of law, “one of the fundamental principles of a democratic society…, which is expressly referred to in the Preamble to the Convention”…. --Sakik and Others v. Turkey, ECHR, 26 November 1997 (para. 44). ***** The Court attaches significance to the fact that, as the intervenors pointed out in connection with Article 13…, in Canada a more effective form of judicial control has been developed in cases of this type. This example illustrates that there are techniques which can be employed which both accommodate legitimate security concerns about the nature and sources of intelligence information and yet accord the individual a substantial measure of procedural justice. It follows that the Court considers that neither the proceedings for habeas corpus and for judicial review of the decision to detain Mr Chahal before the domestic courts, nor the advisory panel procedure, satisfied the requirements of Article 5 para. 4…. This shortcoming is all the more significant given that Mr Chahal has undoubtedly been deprived of his liberty for a length of time [more than three years] which is bound to give rise to serious concern…. --Chahal v. the United Kingdom, ECHR, 15 November 1996 (paras. 131-132). ***** The Court stresses in this respect that the unacknowledged detention of an individual is a complete negation of … guarantees [against arbitrary deprivation of liberty] and a most grave violation of Article 5. Having assumed control over [an] individual, it is incumbent on the authorities to account for his or her whereabouts. For this reason, Article 5 must be seen as requiring the authorities to take effective measures to safeguard against the risk of disappearance and to conduct a prompt effective investigation into an arguable claim that a person has been detained and has not been seen since…. --Orhan v. Turkey, ECHR, 18 June 2002 (para. 369). ***** The Court notes that the applicant's detention in police custody lasted eight days. It recalls that in the Brogan and Others case it held that detention in police custody which had lasted four days and six hours without judicial control fell outside the strict constraints as to the time laid down by Article 5 § 3 of the Convention, even though its purpose was to protect the community as a whole against terrorism…. 43