MLA is an exclusive procedure between two or more sovereign states. So, the main interlocutors of MLA are states. Persons who are party to a criminal proceeding or attorneys or representatives of parties cannot conduct MLA relations but can only trigger the process by asking or directing the court or prosecutorial bodies.
Other than that, international organizations acting as conduits are becoming more and more active in the field to create platforms for MLA and promote its use.
In the national sense, most countries designate central authorities to deal with incoming and outgoing MLA requests, instead of leaving the issue at the hands of local courts or prosecutorial bodies.
There are several reasons behind this. One is to sort out and make the prima facie evaluation of the requests and prioritize them on tailor-made criteria if need be or simply refuse them without having to send them to the courts if they lack the requirements. Imagine, as a practitioner yourself, the workload judges and prosecutors would have if all requests for MLA would come directly.
Second is the need to centralize and unify the MLA practice. Since we established that MLA is in direct relation with sovereignty, we can safely say that it also constitutes a part of the policy of criminal law. A centralized body in MLA would be more efficient in formulating and applying this aspect of the policy of criminal law. A centralized body will also serve to unify the national practice.
For more information on central authorities, please check out the IIJ’s Global Central Authorities Initiative and IIJ Good Practices for Central Authorities, which can be accessed here.
Last but not least, central authorities are there to provide everything beyond the mandate of courts and prosecutorial bodies and keep track of the request, both incoming and outgoing. As explained before, MLA can rely on the principle of reciprocity, as well as international agreements. And sometimes both.
Central authorities can give or demand guarantees within the scope of MLAs and keep the track record of compliance of other central authorities with their commitments, both within the frame of international agreements or outside.