I have some questions for you. Do you think the person who knows realizes that he knows for sure already or is he still in the hunch phase? And, in your case, why do you think it took that much time? Was it an evidence issue or did you experience that much resistance to your theories?
It's even worse if the LEO only has a good hunch. My guess in La belle was a hunch because the two young girls were THERE. Everybody else was running around saying, for example, "Who was that Arab-looking man in the white leisure suit?" Also, we were looking into every Arab in Berlin. It turned out one of the 2 German girls was married to a Libyan.