Finally, there is a last layer of laws: the domestic implementation of international
instruments. A law on international co-operation in criminal matters is the hyphen
between (ratified) international instruments and domestic criminal (procedure) law.
This law is where the parties meet when they co-operate. The problem identified in
practice is that despite the efforts towards harmonisation through international
instruments, each state tends to implement conventions in a different way. The variety of laws operating according to different terms and conditions renders
international co-operation more complex, and thus less attractive. Domestic
legislation in this field should include consultations with other states and the inclusion
of comparative law with a view to achieving the highest harmonisation possible.