Ch lll of the constitution Chapter Ill of the Constitution may not appear at first glance to be fertile ground for arguments based on international law. However, international law has had some relevance in determining whether Ch Ill precludes the enactment of ex post facto criminal laws and, if it does, precisely what amounts to such a law. These issues were raised in Polyukhovich, which concerned the validity of the Commonwealth War Crimes Act. Deane J concluded that Ch Ill did preclude ex post facto criminal laws and, although his Honour's decision was based primarily on his conception of the nature of the judicial process, he also drew support from international human rights conventions, such as the European Convention for the Protection of Human Rights (ECHR) and the American Convention on Human Rights, which provided protection against the imposition of retrospective criminal guilt. Australia is not a party to either of these conventions, but Deane J used them to support his conclusion that"ex post facto criminal legislation lies outside the proper limits of the legislative function as a matter of principle. 28 Both Deane J and Gaudron J also made use of principles of international law in their application of the prohibition on ex post facto criminal laws stemming from Ch lll of the Constitution. Because they concluded that such a prohibition existed, it was necessary for them to establish whether the War Crimes Act violated the prohibition It was accepted that the conduct criminalised by the act was not criminal in domestic law at the time of its commission; however, both judges considered it necessary to (1991)172CLR501,611-2 /bid 612 bid 6111. Ch III of the Constitution Chapter III of the Constitution may not appear at first glance to be fertile ground for arguments based on international law. However, international law has had some relevance in determining whether Ch III precludes the enactment of ex post facto criminal laws and, if it does, precisely what amounts to such a law. These issues were raised in Polyukhovich, which concerned the validity of the Commonwealth War Crimes Act. Deane J concluded that Ch III did preclude ex post facto criminal laws26 and, although his Honour’s decision was based primarily on his conception of the nature of the judicial process, he also drew support from international human rights conventions, such as the European Convention for the Protection of Human Rights (“ECHR”) and the American Convention on Human Rights, which provided protection against the imposition of retrospective criminal guilt.27 Australia is not a party to either of these conventions, but Deane J used them to support his conclusion that “ex post facto criminal legislation lies outside the proper limits of the legislative function” as a matter of principle.28 Both Deane J and Gaudron J also made use of principles of international law in their application of the prohibition on ex post facto criminal laws stemming from Ch III of the Constitution. Because they concluded that such a prohibition existed, it was necessary for them to establish whether the War Crimes Act violated the prohibition. It was accepted that the conduct criminalised by the Act was not criminal in domestic law at the time of its commission; however, both judges considered it necessary to 26 (1991) 172 CLR 501, 611-2. 27 Ibid 612. 28 Ibid 611. 6