80 GIULIANI AND GAGGIO v. ITALY JUDGMENT see, for example, Tanrıkulu v. Turkey [GC], no. 23763/94, § 109, ECHR 1999-IV; as regards forensic examinations, see, for example, Gül v. Turkey, no. 22676/93, § 89, 14 December 2000). Any deficiency in the investigation which undermines its ability to establish the cause of death or the person responsible will risk falling foul of this standard (see Avşar, cited above, §§ 393-395). 302. In particular, the investigation's conclusions must be based on thorough, objective and impartial analysis of all relevant elements. Failing to follow an obvious line of inquiry undermines to a decisive extent the investigation's ability to establish the circumstances of the case and the identity of those responsible (see Kolevi, cited above, § 201). Nevertheless, the nature and degree of scrutiny which satisfy the minimum threshold of the investigation's effectiveness depend on the circumstances of the particular case. They must be assessed on the basis of all relevant facts and with regard to the practical realities of investigation work (see Velcea and Mazăre v. Romania, no. 64301/01, § 105, 1 December 2009). 303. In addition, the investigation must be accessible to the victim's family to the extent necessary to safeguard their legitimate interests. There must also be a sufficient element of public scrutiny of the investigation, the degree of which may vary from case to case (see Hugh Jordan, cited above, § 109, and Varnava and Others v. Turkey [GC], nos. 16064/90, 16065/90, 16066/90, 16068/90, 16069/90, 16070/90, 16071/90, 16072/90 and 16073/90, § 191, ECHR 2009-...; see also Güleç, cited above, § 82, where the victim's father was not informed of the decision not to prosecute, and Oğur, cited above, § 92, where the family of the victim had no access to the investigation or the court documents). 304. However, disclosure or publication of police reports and investigative materials may involve sensitive issues with possible prejudicial effects to private individuals or other investigations and, therefore, cannot be regarded as an automatic requirement under Article 2. The requisite access of the public or the victim's relatives may therefore be provided for in other stages of the procedure (see, among other authorities, McKerr v. the United Kingdom, no. 28883/95, § 129, ECHR 2001-III). Moreover, Article 2 does not impose a duty on the investigating authorities to satisfy every request for a particular investigative measure made by a relative in the course of the investigation (see Ramsahai and Others [GC], cited above, § 348, and Velcea and Mazăre, cited above, § 113). 305. A requirement of promptness and reasonable expedition is implicit in this context (see Yaşa v. Turkey, 2 September 1998, §§ 102-104, Reports 1998-VI; Tanrıkulu, cited above, § 109; and Mahmut Kaya v. Turkey, no. 22535/93, §§ 106-107, ECHR 2000-III). It must be accepted that there may be obstacles or difficulties which prevent progress in an investigation in a particular situation. However, a prompt response by the authorities in investigating a use of lethal force may generally be regarded as essential in