152. That being said, the Court considers it useful in the present case to clarify the general principles concerning the examination of defence witnesses as formulated in its case-law under Article 6 §§ 1 and 3 (d) of the Convention.
153. The applicable Perna test consists of two questions: firstly, whether the applicant has substantiated his or her request to call a particular witness by referring to the relevance of that individual’s testimony for “the establishment of the truth” and, secondly, whether the domestic courts’ refusal to call that witness undermined the overall fairness of the proceedings (see paragraph 141 above).
154. However, a careful study of the case-law reveals that despite generally following the above approach the Court has also consistently examined the manner in which the domestic courts decided on a request to call a certain witness. The conduct and decision-making of the domestic courts have attracted independent scrutiny and were weighty factors in the Court’s analysis in the great majority of pre- and post-Perna cases (see, among many other examples, Bricmont, cited above, § 89; Destrehem v. France, no. 56651/00, §§ 41-45, 18 May 2004; Asci v. Austria (dec.), no. 4483/02, 19 October 2006; Popov, cited above, § 188; Polyakov, cited above, § 35; Tarău v. Romania, no. 3584/02, §§ 74-76, 24 February 2009; and Topić, cited above, § 42). The Court’s careful and deferential examination of the domestic courts’ reasoning is in line with the established principles that, firstly, those courts are best placed to assess the relevance and admissibility of evidence and, secondly, that only exceptional circumstances will prompt the Court to conclude that the failure to hear a particular person as a witness was incompatible with Article 6 of the Convention.
155. Therefore the question whether the domestic courts considered the relevance of that individual’s testimony and provided sufficient reasons for their decision not to examine a witness at trial must be recognised as an independent and integral component of the test under Article 6 § 3 (d) of the Convention.
156. It appears that the judicial assessment of the relevance of a witness’ testimony and the reasoning of the domestic courts in their response to the defence’s request to examine a witness provide the logical link between the two elements of the Perna test and have operated as an implicit substantive element of that test. The Court considers it desirable in the interests of clarity and consistency of practice to make this element explicit (see, similarly, Perez v. France [GC], no. 47287/99, § 54-56, ECHR 2004‑I).
157. This development appears to be in line with the recent case-law under Article 6 of the Convention stressing the decisive importance of the domestic courts’ duty to engage in a careful scrutiny of the relevant issues if the defence advances a sufficiently reasoned claim. For example, the Court in the Grand Chamber judgment in the case of Dvorski v. Croatia ([GC], no. 25703/11, § 109, ECHR 2015) maintained that when the domestic authorities are presented with a legal challenge which might influence the overall fairness of the proceedings they must engage in a careful scrutiny of the issues, take steps to establish the relevant circumstances, and provide reasons adequate for their decisions. In a similar way, in agent provocateur cases the Court has stated that when “confronted with a plausible – and even arguable – allegation” of entrapment the courts “should have had regard to whether the results of the test purchases were admissible as evidence, in particular verifying that they were not tainted by incitement” (see Lagutin and Others v. Russia, nos. 6228/09 and 4 others, § 118, 24 April 2014).
158. Where a request for the examination of a witness on behalf of the accused has been made in accordance with domestic law, the Court, having regard to the above considerations, formulates the following three-pronged test:
1. Whether the request to examine a witness was sufficiently reasoned and relevant to the subject matter of the accusation?
2. Whether the domestic courts considered the relevance of that testimony and provided sufficient reasons for their decision not to examine a witness at trial?
3. Whether the domestic courts’ decision not to examine a witness undermined the overall fairness of the proceedings?
159. The Court considers that the existing case-law already provides a solid basis for the application of all three steps of the test, but finds it appropriate to provide the following guidance for the examination of future cases.
(a) Whether the request to examine a witness was sufficiently reasoned and relevant to the subject matter of the accusation
160. In respect of the first element the Court notes that under the Perna test the issue of whether an accused substantiated his or her request to call a witness on his or her behalf is decided by reference to the relevance of that individual’s testimony for “the establishment of the truth”. While certain post-Perna cases examined whether a witness’ testimony was relevant for the “establishment of the truth”, others relied on its ability to influence the outcome of a trial (see Tarasov, cited above, § 105), reasonably establish an accused’s alibi (see Polyakov, cited above, § 34), arguably lead to an acquittal (see Dorokhov, cited above, § 72) or arguably strengthen the position of the defence or even lead to the applicant’s acquittal (see Topić, cited above, § 42). What appears to unite all of the above standards is the relevance of a witness’s testimony to the subject matter of the accusation and its ability to influence the outcome of the proceedings. In the light of the evolution of its case-law under Article 6 of the Convention the Court considers it necessary to clarify the standard by bringing within its scope not only motions of the defence to call witnesses capable of influencing the outcome of a trial, but also other witnesses who can reasonably be expected to strengthen the position of the defence.
161. The relevance of testimony is thus also determinative of the assessment of whether an applicant has advanced “sufficient reasons” for his or her request to call a witness, since the strength of reasoning considered “sufficient” depends on the role of that testimony in the circumstances of any given case (see Pello, cited above, § 33, largely reflecting this approach). It is impossible to evaluate in the abstract whether certain reasons for the examination of a witness could be considered sufficient and relevant to the subject matter of the accusation. This assessment necessarily entails consideration of the circumstances of a given case, including the applicable provisions of the domestic law, the stage and progress of the proceedings, the lines of reasoning and strategies pursued by the parties and their procedural conduct. Admittedly, the relevance of a defence witness’ testimony might be so apparent in certain cases that even scant reasoning given by the defence would be sufficient to answer the first question of the test in the affirmative (compare Pello, cited above, § 33).
(b) Whether the domestic courts considered the relevance of that testimony and provided sufficient reasons for their decision not to examine a witness at trial
162. The second element of the test requires the domestic courts to consider the relevance of the testimony sought by the defence and obliges them to provide sufficient reasons for their decisions. These requirements are well-established in the Court’s case-law (see, for example, Popov, cited above, § 188, and Topić, cited above, § 42).
163. The Court reiterates that, on the one hand, under Article 6 of the Convention the admissibility of evidence is primarily a matter for regulation by national law and the domestic courts are best placed to decide on the issue and, on the other hand, Article 6 § 3 (d) of the Convention does not require the attendance and examination of every witness on the accused’s behalf, but aims to ensure equality of arms in the matter. Within this framework it is primarily for the domestic courts to scrutinise carefully the relevant issues if the defence advances a sufficiently reasoned request to examine a certain witness.
164. Any such assessment would necessarily entail consideration of the circumstances of a given case and the reasoning of the courts must be commensurate, i.e. adequate in terms of scope and level of detail, with the reasons advanced by the defence.
165. Since the Convention does not require the attendance and examination of every witness on behalf of the accused, the courts cannot be expected to give a detailed answer to every motion of the defence but must provide adequate reasons (for a similar logic in the context of the courts’ obligation to address appeal arguments, see Van de Hurk v. the Netherlands, 19 April 1994, § 61, Series A no. 288, and Boldea v. Romania, no. 19997/02, § 30, 15 February 2007).
166. Generally the relevance of testimony and the sufficiency of the reasons advanced by the defence in the circumstances of the case will determine the scope and level of detail of the domestic courts’ assessment of the need to ensure a witness’ presence and examination. Accordingly, the stronger and weightier the arguments advanced by the defence, the closer must be the scrutiny and the more convincing must be the reasoning of the domestic courts if they refuse the defence’s request to examine a witness.
(c) Whether the domestic courts’ decision not to examine a witness undermined the overall fairness of the proceedings
167. The Court considers that the examination of the impact which a decision refusing to examine a defence witness at the trial has on the overall fairness of the proceedings is indispensable in every case (see, in different contexts, Ibrahim and Others v. the United Kingdom [GC], nos. 50541/08 and 3 others, §§ 250-52, 13 September 2016; Dvorski, cited above, § 82; and Schatschaschwili, cited above, § 101). Compliance with the requirements of a fair trial must be examined in each case having regard to the development of the proceedings as a whole and not on the basis of an isolated consideration of one particular aspect or one particular incident (see Ibrahim and Others, cited above, § 251).
168. In the Court’s opinion, the preservation of overall fairness as the final benchmark for the assessment of the proceedings ensures that the above three-pronged test does not become excessively rigid or mechanical in its application. While the conclusions under the first two steps of that test would generally be strongly indicative as to whether the proceedings were fair, it cannot be excluded that in certain, admittedly exceptional, cases considerations of fairness might warrant the opposite conclusion.“