64 GIULIANI AND GAGGIO v. ITALY JUDGMENT 245. That does not mean, however, that a positive obligation to prevent every possibility of violence can be derived from this provision. The obligation in question must be interpreted in a way which does not impose an impossible or disproportionate burden on the authorities, bearing in mind the difficulties involved in policing modern societies, the unpredictability of human conduct and the operational choices which must be made in terms of priorities and resources (see Osman, cited above, § 116, and Maiorano and Others v. Italy, no. 28634/06, § 105, 15 December 2009). 246. Accordingly, not every claimed risk to life can entail for the authorities a Convention requirement to take operational measures to prevent that risk from materialising. The Court has held that a positive obligation will arise where the authorities knew or ought to have known of the existence of a real and immediate risk to the life of an identified individual or individuals and failed to take measures within the scope of their powers which, judged reasonably, might have been expected to avoid that risk (see Bromiley v. the United Kingdom (dec.), no. 33747/96, 23 November 1999; Paul and Audrey Edwards v. the United Kingdom, no. 46477/99, § 55, ECHR 2002-II; and Branko Tomašić, cited above, §§ 50-51). 247. In this connection it should be pointed out that in Mastromatteo (cited above, § 69), the Court drew a distinction between cases concerning the requirement of personal protection of one or more individuals identifiable in advance as the potential target of a lethal act (see Osman and Paul and Audrey Edwards, both cited above; see also the judgments adopted in the wake of Mastromatteo, namely Branko Tomašić, cited above, and Opuz, cited above), and those in which the obligation to afford general protection to society was in issue (see Maiorano and Others, cited above, § 107). 248. Furthermore, for the State's responsibility under the Convention to be engaged, it must be established that the death resulted from a failure on the part of the national authorities to do all that could reasonably be expected of them to avoid a real and immediate risk to life of which they had or ought to have had knowledge (see Osman, cited above, § 116; Mastromatteo, cited above, § 74; and Maiorano and Others, cited above, § 109). 249. According to its case-law, the Court must examine the planning and control of a policing operation resulting in the death of one or more individuals in order to assess whether, in the particular circumstances of the case, the authorities took appropriate care to ensure that any risk to life was minimised and were not negligent in their choice of action (see McCann and Others, cited above, §§ 194 and 201, and Andronicou and Constantinou, cited above, § 181). The use of lethal force by police officers may be justified in certain circumstances. Nonetheless, Article 2 does not grant a carte blanche. Unregulated and arbitrary action by State agents is