Article 9 para 2 of the Directive 2014/41/EU of 3 April 2014 on the European Investigation Order:” The executing authority shall comply with the formalities and procedures expressly indicated by the issuing authority unless otherwise provided in this Directive and provided that such formalities and procedures are not contrary to the fundamental principles of law of the executing State.”
Most of the international agreements prescribe the possibilities of conducting requested investigative measure in accordance with the law of requesting state. For example, Article 8 of the Second Additional Protocol to the European Convention on mutual legal assistance in criminal matters prescribes the following:
“Notwithstanding the provisions of Article 3 of the Convention, where requests specify formalities or procedures which are necessary under the law of the requesting Party, even if unfamiliar to the requested Party, the latter shall comply with such requests to the extent that the action sought is not contrary to fundamental principles of its law, unless otherwise provided for in this Protocol.2
In the absence of the international agreement the rule of reciprocity is being applied as well as domestic law.
In accordance with the Article 10 of the Act on mutual legal assistance in criminal matters the Republic of Croatia as requesting state can execute service in accordance with the law of requesting state:
(1) When providing international legal assistance, the domestic judicial body will comply with the formalities and procedures that are explicitly stated in the application as necessary according to the law of the requesting state, unless an international treaty provides otherwise and on the condition that such formalities and procedures do not contradict the principles domestic legal order.
(2) The domestic judicial body decides upon the request of the foreign judicial body without delay, taking into account procedural deadlines and other specially determined deadlines explained in the request.