The ECtHR assesses the fairness of the proceedings as a whole. In Doorson v the Netherlands, judgment of 26 March 1996, paras 69 to 76, it found the use of anonymous witnesses compatible with Article 6 on the safeguards present in that case. The defence could put questions unless they risked revealing identity. The Court also stated that a conviction should not be based solely or decisively on anonymous statements.
Van Mechelen and Others v the Netherlands, judgment of 23 April 1997, paras 56 to 66, reached a different result on its facts. The defence faced severe restrictions on questioning and could not observe the witnesses; their statements carried particular weight. The Court found that the disadvantages had not been sufficiently offset and held that Article 6 had been violated.
These judgments establish neither automatic admissibility nor an automatic exclusion rule. They focus attention on the reasons for protection, the questions actually available, other safeguards and the weight of the statement in the full evidential picture.