1.1. Principle locus regit actum. The locus regit actum principle conventionally governs the execution of mutual assistance requests whom the judicial authorities of a State refer when they need to collect evidence in the territory of another State. 1.2. Formulation. In Europe, this principle is formulated by the European Convention on Mutual Assistance in Criminal Matters of 20 April 1959. Article 3 provides that "the requested Party shall execute, in the manner provided for by its law any letters rogatory relating to a criminal matter and addressed to it by the judicial authorities of the requesting Party (…)".