Abstract: In a public switched telephone network, interoffice call attempts to or from a line under surveillance generate a variety of query, response and release messages between the offices, as part of the normal procedures for setting up and tearing down the calls to and from the line. To insure that all calls under surveillance generate signaling messages, terminating, dialing and release triggers are set with respect to the target's line. As a result, the end office serving that line sends queries to a database on the signing network, receives response messages, and sends release report messages. A site processor compiles data from the signaling messages and forms a call detail record (CDR) for each call attempt relating to the target under surveillance. A central file server further processes the CDRs and supplies composite data regarding the target's calls through a data network connection to one or more law enforcement agencies.