Researchers have found a relationship between word choices in communications and how well a relationship is functioning. In other words, content in communications can be used to establish the overall health of a relationship: http://www.msnbc.msn.com/id/28814669/

If the choice of words can be used to determine the strength of a relationship based on frequency of certain words, it is not a far conclusion to be drawn that foul play could be found by the same type of study. The choice of words would be different of course, but if there was a large collection of communications that could be mined between criminals, it should be possible to use pattern recognition to ferret out such communications in network traffic.