The second category of questions relates to the admissibility of evidence obtained by the National Crime Authority from a witness during a s 25 hearing when the witness is subsequently tried on an indictment charging him with a criminal offence. In the criminal proceedings against the respective respondents pending in the Supreme Court of Victoria, Vincent J has ruled that, as the matter into which the National Crimes Authority was conducting a hearing when the relevant statements were made by the respective respondents did not empower the Authority to compel the giving of the evidence now sought to be tendered against them, that evidence was not given voluntarily. His Honour thus ruled that the evidence is not admissible on their trial. And that, despite the provisions of s 30(4) of the National Crime Authority Act which entitles a natural person to refuse to answer questions or to refuse to produce documents on the ground that the answer to the question or the production of the document might tend to incriminate that person. Whether such ruling is correct in law is an important question. It raises the question whether a purported but invalid exercise of power to compel the giving of evidence necessitates the conclusion that any evidence given is involuntary and, for that or any other reason, inadmissible. In an appropriate case, that question would warrant a grant of special leave.