"In any event, bearing in mind the concept of fairness in Article 6, the right not to incriminate oneself cannot reasonably be confined to statements of admissions or remarks which are directly incriminating. Testimony obtained under compulsion which appears on its face to be of a non-incriminating nature, such as exculpatory remarks or information on questions of fact, may later be deployed in criminal proceedings in support of the prosecution case, for example, to contradict or cast doubt upon other statements of the accused or evidence given by him during the trial or to otherwise undermine his credibility. Where the credibility of an accused must be assessed by a jury, the use of such testimony may be especially harmful. It follows that what is of the essence in this context is the use to which evidence obtained at a compulsion is put in the course of the criminal trial."