The place where the psychics thought that Rhonda's body was dumped re: north Mountain, is a vast area, which many large plots of and 300 and 400 acres are privately owned, and the areas are heavily wooded.
My guess if the family might know the person responsible, it to check the properties he might own, or his relatives, or old haunts, i.e. anyplace he might hunt, hang around as a child, etc. This is the usual way
perps work. Grandparents, aunts uncles, cousins property..... The burden of proof, nothing like a good sting set up by police, i.e. Clarissa Boudreau's case