84 A. AND OTHERS v. THE UNITED KINGDOM JUDGMENT difficulties this caused were counterbalanced in such a way that each applicant still had the possibility effectively to challenge the allegations against him. 219. The Court considers that SIAC, which was a fully independent court (see paragraph 91 above) and which could examine all the relevant evidence, both closed and open, was best placed to ensure that no material was unnecessarily withheld from the detainee. In this connection, the special advocate could provide an important, additional safeguard through questioning the State’s witnesses on the need for secrecy and through making submissions to the judge regarding the case for additional disclosure. On the material before it, the Court has no basis to find that excessive and unjustified secrecy was employed in respect of any of the applicants’ appeals or that there were not compelling reasons for the lack of disclosure in each case. 220. The Court further considers that the special advocate could perform an important role in counterbalancing the lack of full disclosure and the lack of a full, open, adversarial hearing by testing the evidence and putting arguments on behalf of the detainee during the closed hearings. However, the special advocate could not perform this function in any useful way unless the detainee was provided with sufficient information about the allegations against him to enable him to give effective instructions to the special advocate. While this question must be decided on a case-by-case basis, the Court observes generally that, where the evidence was to a large extent disclosed and the open material played the predominant role in the determination, it could not be said that the applicant was denied an opportunity effectively to challenge the reasonableness of the Secretary of State’s belief and suspicions about him. In other cases, even where all or most of the underlying evidence remained undisclosed, if the allegations contained in the open material were sufficiently specific, it should have been possible for the applicant to provide his representatives and the special advocate with information with which to refute them, if such information existed, without his having to know the detail or sources of the evidence which formed the basis of the allegations. An example would be the allegation made against several of the applicants that they had attended a terrorist training camp at a stated location between stated dates; given the precise nature of the allegation, it would have been possible for the applicant to provide the special advocate with exonerating evidence, for example of an alibi or of an alternative explanation for his presence there, sufficient to permit the advocate effectively to challenge the allegation. Where, however, the open material consisted purely of general assertions and SIAC’s decision to uphold the certification and maintain the detention was based solely or to a decisive degree on closed material, the procedural requirements of Article 5 § 4 would not be satisfied.