Directive 2014/41/EU regarding the European Investigation Order in criminal matters. It is applicable in relation to the Member States, which have also implemented the EIO Directive. For the countries, which have not implemented the EIO Directive so far, the following legal framework is applicable: European Convention on Mutual Assistance in Criminal Matters of April 20, 1959. (Art11(1).
Directive 2014/41/EU on EIOs (Art. 3);
Art 11(1) 1959 Convention