Anonymous MANET routing relies on techniques such as re-encryption on each hop to hide end-to-end communication relations. However, passive signal detectors and traffic analyzers can still retrieve sensitive information from PHY and MAC layers through statistical traffic analysis. In this paper, we propose a statistical traffic pattern discovery (STPD) system. STPD intends to find out the sources and destinations of captured packets and discover the end-to-end communication relations. The proposed approach does not require analyzers to be actively involved in MANET transmissions or to decrypt the traffic. We present theoretical models as well as extensive simulations to demonstrate our solutions.