31 Part 1 The following set of principles reflects international good practices on how to process data in compliance with international human rights standards: • Data must be collected and processed fairly and lawfully; • Data must be collected for a determined, explicit and legitimate purpose, and must not be subsequently processed in a manner incompatible with this purpose; • The data collected must be adequate, relevant and non-excessive for the purposes for which they were collected and subsequently processed; • The data must be accurate, complete and up-to-date; • The data must be stored in a form that allows the identification of their subjects; • The relevance and accuracy of the data must be regularly evaluated; data that are inaccurate or no longer relevant for the purposes for which they were obtained and stored must be updated or deleted; and • The collection and processing of data should be subject to supervision by an external independent authority. 41 It should be borne in mind that some material that might normally be expected to be subject to weeding may need to be kept for an extended period if it has been used as part of a criminal prosecution. While information may have been gathered primarily for intelligence purposes, there is always the possibility that it has to be turned into evidence or form the basis of evidence. If a concrete court case should be made, nothing of this nature should be deleted but, instead, it should be handled appropriately in adequate systems until the case has come to trial and any period for which an appeal may be lodged has elapsed. Otherwise a violation of the right to a fair trial may occur. 41 41 Ibid, practice 24, para. 38. See also Council of Europe, Convention for the Protection of Individuals with regard to Automatic Processing of Personal Data, Strasbourg, 28 January 1981, Article 5, <http://conventions.coe.int/Treaty/en/Treaties/Html/108.htm>, and Council of Europe Committee of Ministers, Recommendation R (87) 15E on regulating the use of personal data in the police sector, Strasbourg, 17 September 1987, <https:// wcd.coe.int/ViewDoc.jsp?id=704881&Site=CM>.