I agree with Cherry. I think the person responsible for Bob's disappearance is someone who did not want his new wife's name signed onto his accounts and will, therefore keeping her out of Bob's millions and it's most likely parricide.
It's been a while since I saw his episode of Disappeared, but I don't remember his daughters being too pleased about their father's decisions about the marriage and about signing Fontelle onto his accounts. As I said though I might be remembering things wrong, but they always seemed annoyed at Fontelle.
Cases are hard to prove without a body, unfortunately and my heart really breaks for Fontelle. She deserves to have closure and to know where Bob is.
I can only hope the LE are building a case and that's why things have gone quiet!
I'm interested if anyone knows this - Fontelle was meant to live with Bob permanently after returning from Missouri one last time but then he disappeared. Does she still live in Bob's home in California or did she move back to Missouri?
Another thing - did they ever do forensics on Bob's house? Did the housekeeper ever say she heard any sounds inside the house while she was waiting? I'm wondering if an altercation occurred in the house.