Methods for determining a cause of a detected anomalous event in a telecommunications system are provided. The methods include detecting an anomalous event in the telecommunications system and retrieving relevant call detail record (CDR) data associated with the detected anomalous event for at least one identified time interval responsive to detecting the anomalous event. The relevant CDR data includes both current CDR data for the at least one identified time interval and historical CDR data for past intervals corresponding to the at least one identified time interval. The relevant CDR data including the current CDR data and the historical CDR data is preprocessed and the preprocessed relevant CDR data is processed to determine a root cause of the detected anomalous event. Processing the preprocessed relevant CDR data includes comparing the current CDR data and the historical CDR data to determine the root cause of the detected anomalous event.