Detention: extent and concerns, including radicalisation of becoming radicalised are included in the mentoring programme.148 The best way to prevent radicalisation in prison is likely genuinely good prison management that effectively addresses fundamental rights problems and ensures that social rehabilitation is taken very seriously from the very outset of the sentence served. Conclusion and FRA Opinion International human rights law requires making pretrial detention – when a suspect has not yet been found guilty – the exception rather than the rule. For example, Article 6.1 of the UN Standard Minimum Rules for NonCustodial Measures (the so-called Tokyo Rules) refers to pre-trial detention as a means of “last resort”. Similarly, Article 37 (b) of the UN Convention on the Rights of the Child provides that detention of children shall be a measure of last resort, and Article 5 of the European Convention on Human Rights (ECHR) outlines limitations on the use of detention generally. UN and European experts and expert bodies warn against the overuse of detention. Detention should be used as penalty for crimes against individuals and society, to deter potential offenders from committing crimes, and to protect victims and society. Compared to data relating to the specific Framework Decisions covered in this study, existing data and information on detention in the EU Member States are rather good, with the Council of Europe providing particularly useful sources. Further harmonisation of categories, even such basic aspects as what constitutes pre-trial detention, would certainly still be needed to improve the quality and level of detail of the data, and, as has been stated, more could be done to make the data and information more accessible. While the use of detention varies significantly across EU Member States, according to FRA’s comparison, the average across the 28 is reasonable when compared globally. However, in several EU Member States, and to some extent in all of them, detention could and should be used less. The number of persons in detention who are from other EU Member States (and the proportion of these) logically also varies significantly across the EU. But there is a potential for greater use of the three Framework Decisions, more so in some EU Member States than in others. According to the data analysed by FRA and the information available from international monitoring mecha­ nisms, fundamental rights-related problems with detention in the EU include – in addition to over-use – overcrowding and poor detention conditions. This can undermine mutual trust, and also undermine a central goal of the three Framework Decisions: to enhance social rehabilitation. FRA Opinion 5 To ensure effective implementation of the three Framework Decisions, the  EU and its Member States need to take further action. Pre-trial detention must be reduced in many Member States to comply with international human rights standards and, as stated, to avoid discrimination on the basis of nationality. A  general reduction of detention must also be sought to avoid overcrowding, which can lead to poor prison conditions. The interests of society in terms of the financial costs of detention and poorly rehabilitated former detainees must also be considered. To facilitate this, transfers of best practices and full use of the Framework Decisions are needed. 148 European Network of Deradicalisation; European Commission, DG Migration and Home Affairs. 59