The method provides a Law Enforcement Agency LEA with retention or interception data related to a target user. At a data retention source node or at an interception control element of a telecommunications network, traffic packets involving the target user are inspected and a plurality of usage data records based on the inspected traffic packets are generated. Each record comprises information relating to a certain service class and to a respective communications stack layer. For each communications session involving a plurality of different communications stack layers, at the data retention source node or, respectively, the interception control element, the plurality of usage data records are provided with a same correlation identity number for correlating the data at the different communications stack layers. Then, the usage data records comprising the correlation identity number to the LEA are sent, for instance to the LI system or the data Retention System, respectively.