A selection of key paragraphs can be found below the judgment.
60. The Court reiterates that where a person raises an arguable claim or makes a credible assertion that he has suffered treatment contrary to Article 3 at the hands of State agents, that provision, read in conjunction with the general duty under Article 1 of the Convention to “secure to everyone within their jurisdiction the rights and freedoms defined in … [the] Convention”, requires by implication that there should be an effective official investigation (see, among many authorities, Assenov and Others v. Bulgaria, 28 October 1998, § 102, Reports of Judgments and Decisions 1998‑VIII; Labita v. Italy [GC], no. 26772/95, § 131, ECHR 2000-IV, and Bouyid v. Belgium [GC], no. 23380/09, § 124, ECHR 2015).
62. The Court has also held that the investigation should be capable of leading to the identification and punishment of those responsible. If not, the general legal prohibition of torture and inhuman and degrading treatment and punishment would, despite its fundamental importance, be ineffective in practice and it would be possible in some cases for State agents to abuse the rights of those within their control with virtual impunity (see Labita, cited above, § 131). The investigation must also be thorough: the authorities must always make a serious attempt to find out what happened and should not rely on hasty or ill-founded conclusions to close their investigation or as the basis of their decisions. Furthermore, the investigation must be prompt and independent. Lastly, it must afford a sufficient element of public scrutiny to secure accountability. While the degree of public scrutiny required may vary, the complainant must be afforded effective access to the investigatory procedure in all cases (see Batı and Others v. Turkey, nos. 33097/96 and 57834/00, § 137, ECHR 2004-IV, and Krsmanović v. Serbia, no. 19796/14, § 74, 19 December 2017).
63. Turning to the present case, the Court considers that the applicant’s complaint of police abuse was such as to require an effective official investigation (see paragraphs 11 and 12 above), it being noted that even where there is insufficient evidence to show that an applicant had in fact been ill-treated the procedural obligation to investigate may still arise, particularly when, such as in the present case, there is a potential for abuse in a detention context (see, mutatis mutandis, Stepuleac v. Moldova, no. 8207/06, § 64, 6 November 2007).
64. (…) Yet, despite the Convention and the domestic law requiring that an allegation of this sort be examined ex officio (see paragraphs 61 and 39 above, in that order), no separate abuse-related investigation aimed at the identification and punishment of those responsible was ever instituted by the relevant authorities. The criminal case against the applicant, wherein he raised his abuse complaints in order to have some of the impugned evidence excluded, was certainly not capable of the latter (see, regarding precisely this point, Hajnal v. Serbia, no. 36937/06, § 99, 19 June 2012, and Lakatoš and Others v. Serbia, no. 3363/08, § 82, 7 January 2014).