AUAD v. BULGARIA JUDGMENT 13 (b) the third-country national concerned avoids or hampers the preparation of return or the removal process. Any detention shall be for as short a period as possible and only maintained as long as removal arrangements are in progress and executed with due diligence. ... 4. When it appears that a reasonable prospect of removal no longer exists for legal or other considerations or the conditions laid down in paragraph 1 no longer exist, detention ceases to be justified and the person concerned shall be released immediately. 5. Detention shall be maintained for as long a period as the conditions laid down in paragraph 1 are fulfilled and it is necessary to ensure successful removal. Each Member State shall set a limited period of detention, which may not exceed six months. 6. Member States may not extend the period referred to in paragraph 5 except for a limited period not exceeding a further twelve months in accordance with national law in cases where regardless of all their reasonable efforts the removal operation is likely to last longer owing to: (a) a lack of cooperation by the third-country national concerned, or (b) delays in obtaining the necessary documentation from third countries.” 49. On 10 August 2009 the Sofia City Administrative Court made a reference for a preliminary ruling by the European Court of Justice (“ECJ”), enquiring about the construction to be put on various paragraphs of that Article. 50. In his opinion, Advocate General Mazák expressed the view, inter alia, that it was important to note that the periods laid down in Article 15 §§ 5 and 6 of the Directive defined only the absolute and outside limits of the duration of detention, that it was clear from their wording that any detention prior to removal must be for as short a period as possible and may be maintained only as long as removal arrangements are in progress and executed with due diligence, and that detention must be brought to an end when the conditions for detention no longer exist or when there is no longer any reasonable prospect of removal. He went on to say that those maximum periods of detention were part of a body of rules intended to ensure that detention is proportionate, in other words that its duration is for as short a period as possible and, in any event, not for longer than the six months or the eighteen months provided for. 51. In its judgment of 30 November 2009 (Saïd Shamilovich Kadzoev v. Direktsia ‘Migratsia’ pri Ministerstvo na vatreshnite raboti, case C-357/09), the ECJ noted, inter alia, that the objective of Article 15 §§ 5 and 6 was to guarantee in any event that detention for the purpose of removal does not exceed eighteen months. It went on to rule that those