Criminal investigation of serious and organized cross-border environmental crimes requires effective police cooperation. However, the mounting of coordinated and systematic efforts in this field still proves to be difficult. The first explanation for this is the lack of a globally applicable legal framework for mutual assistance in criminal matters. Another important and often underestimated reason is practical problems regarding the exchange of information about detected cross-border environmental crimes and setting up a coordinated criminal investigation in two or more countries in response, as well as with regard to the execution of requests for mutual legal assistance. Legal scholars often assume that enhancing the legal framework for cross-border police cooperation is the primary solution to the problems experienced. Here, I show that practical considerations are just as important for effective cooperation in cases of transnational environmental crime. A specific problem is the fact that this type of crime regularly involves countries with non-democratic regimes or even a non-existent central government, as well as weak law enforcement, both in terms of capabilities and integrity, and consequently law enforcement agencies in other countries will often be reluctant to seek legal assistance.