(a) When the offences are committed in any territory under its jurisdiction or on board a ship or aircraft registered in that State; (b) When the alleged offender is a national of that State; (c) When the victim is a national of that State if that State considers it appropriate. 2. Each State Party shall likewise take such measures as may be necessary to establish its jurisdiction over such offences in cases where the alleged offender is present in any territory under its jurisdiction and it does not extradite him pursuant to article 8 to any of the States mentioned in paragraph 1 of this article. 3. This Convention does not exclude any criminal jurisdiction exercised in accordance with internal law. Article 6 1. Upon being satisfied, after an examination of information available to it, that the circumstances so warrant, any State Party in whose territory a person alleged to have committed any offence referred to in article 4 is present shall take him into custody or take other legal measures to ensure his presence. The custody and other legal measures shall be as provided in the law of that State but may be continued only for such time as is necessary to enable any criminal or extradition proceedings to be instituted. 2. Such State shall immediately make a preliminary inquiry into the facts. 3. Any person in custody pursuant to paragraph 1 of this article shall be assisted in communicating immediately with the nearest appropriate representative of the State of which he is a national, or, if he is a stateless person, with the representative of the State where he usually resides. 4. When a State, pursuant to this article, has taken a person into custody, it shall immediately notify the States referred to in article 5, paragraph 1, of the fact that such person is in custody and of the circumstances which warrant his detention. The State which makes the preliminary inquiry contemplated in paragraph 2 of this article shall promptly report its findings to the said States and shall indicate whether it intends to exercise jurisdiction. 51