l'm surprised that once the case broke that they didn't bring cadaver dogs in, or maybe they did? Cadaver K9s can detect trace amounts of material, for example: small amounts of blood soaked into the ground, teeth, skin sheds, etc.
Even crime scenes that have been "cleaned" can get hits from cadaver dogs. Depends on how good the K9 is, how well the area has been "cleaned", how undisturbed the scene is, etc.
Having hundreds of searchers trample the point last seen provides a challenge for both Trailing and Cadaver K9s. I've seen Trailing K9s that can trail someone that has been riding in a car. But I'm not aware of a Cadaver K9 that can trace a body that has been wrapped in plastic and transported.