ISP server software to track clients browsing

Need a way to track clients browsing child porn to assist our countries cyber crime division in tracking these culprits, the software must be able to track each and every client on our ISP network which is a private network and natted behind a global IP. I want suggestions on what would be the best process, i know installing squid will do this but i want something more in depths with a web based GUI and to keep records. I need this urgently, software must be installed on Centos.