Traffic data monitoring refers to obtaining of confidential identification data regarding a message that has been sent from or received by a network address or terminal end device connected to a public telecommunications network, as well as the temporary disabling of such a connection. The measure may be applied in respect of certain serious offences if the resulting information is assumed to be very important in the investigation. Also information on the location of a mobile communications device may be authorized to be obtained in order to contact a suspect or convicted person. On the consent of the injured party a telecommunications connection in his possession, or use, may also be monitored if it is necessary for the investigation.