I worked a volunteer crime tip line for a while and what many people considered "tips" was beyond belief, calling in dreams, opinions, theories, "visions", and even such things as "I know a man who looks just like the sketch except he is white and has a green VW, not a van", etc. (and these were included in the "tip count" many LE agencies are always quoting.)
We have to remember that while many LE agencies do not have much experience with these cases, they have access to the FBI and any other LEA they may need assistance from, in most cases. If we've thought of it, it is almost a given they have. The truth is, IMO, these types of cases are mostly solved, if at all, by luck, or a valid tip, if hard evidence is not left at the scene. And most victims end up being found by sheer chance, usually via a member of the public going about their day..