15. (1) At any stage of the trial, a Tribunal may with a view to obtaining the evidence of any person supposed to have been directly or indirectly concerned in, or privy to, any of the crimes specified in section 3, tender a pardon to such person on condition of his making a full and true disclosure of the whole of the circumstances within his knowledge relative to the crime and to every other person concerned, whether as principal or abettor, in the commission thereof. (2) Every person accepting the tender under this section shall be examined as a witness in the trial. (3) Such person shall be detained in custody until the termination of the trial.