He was the last one to see her. There was no "person of interest" at the time. No one accused of anything.
I haven't followed this very closely so I am not sure of the timeline etc. I would think that if JVS was the last one to see her, his father probably knew that the police would be interested in talking to him, which might explain why he told him not to help search. Or....if his father knew that he had something to do with it.
After reading your post, I remembered hearing this and just thought I would pass it along...for what it is worth. Either way, it is probably a good thing that JVS didn't participate in the search, there seem to be enough problems with the investigation already.