This isn't a perfect list, but on that topic these are all the recovered missing with vehicles i've been able to find so far (most where the vehicle was missing for atleast 6 months). Not many are suspected to be foul play, though even when they're found it can be hard to say unless there's obvious evidence.
docs.google.com
But I have to agree, after so much time and publicity on this one, if there was evidence for foul play I feel like there would be some movement. There's good reason why water is suspected for these cases.