In addition to a tip, camera, ping, etc leading them to this location, I was thinking maybe something applicable to forensic botany (as they call it), certain type of soil, leaf...something specific to that "nature preserve"...maybe een a type of animal feces or hair...perhaps there were muddy shoes at the house....samples of course would take time to be sent off/ analyzed in a lab etc so perhaps not likely, unless it was something quite obvious, or they had such immediate lab resources available.
The reason I think of this specifically is because of a "Forensic Botanist" in Colorado I saw on TV. She is part of a genius group, forgot their name, who goes out to help recover remains in cold cases, iirc. She was able to locate a body waaay up in a mountain due to isolating a specific type of Aspen tree that only grew there. Iirc, there was something about the way the sun would face in order to facilitate the growth of this particular tree, hence isolating the direction/ spot on the side of the mountain of the remains.
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