Most of the examples used on this site are based on national level concerns. But there are some important categories of crime which involve trans-border issues. In the context of crimes such as international trafficking of migrants or sex workers, or international movements of drugs or stolen property or criminal violations of intellectual property rights the boundaries for estimating the costs of crime have to be widened.
All three principal categories of crime are potentially affected. The consequences of the offence may be spread over a variety of countries, particularly where the activities are multilateral as for example with cyber-crime. Estimates of the consequences have to be made, at least in principle, for all countries affected. The responses to the offences, likewise, might be multilateral. Supporting co-ordinated action across criminal justice agencies across international boundaries can be very costly. Co-operation between national police forces or initiatives such as enabling the issue of arrest warrants across the EU are potentially effective but may be complex to manage. Costs in anticipation of crime, likewise, may arise in a different guise in an international setting. For example, measures to combat VAT fraud in international transactions require a degree of harmonisation across countries that may be costly to devise and may impose substantial compliance (or transactions) costs on legitimate traders.
These kinds of effects are fundamental to questions about the scope for supra-national criminal justice policy making. The basic principles of estimating costs apply equally well in this broader context. The empirical data needed for purposes of cost estimation may impose a formidable challenge. But if these issues are not taken seriously there is a danger that the returns on crime organised internationally will remain high or will grow, and thus induce new entry into such activities.

