I've got errands to run. AND I don't mean to monopolize the thread with just one theory. Anything is still possible and all avenue's should be explored.
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The boat had a security system and the owner, on tv, said nobody had the codes but him.
You could take a car up to that place where the sharks are, don't need a boat.
I don't think it was necessarily Tatoo, and I don't think it is necessarily Croes that points to it, though he's the link to the sea. But if she was disposed of (dead or alive) offshore, which seems likely, and there's no trace of her onshore, then it's likely she went onto a boat willingly, and anybody would like to go for a late night boat ride on a beautiful night their last night in paradise. Even if boat riding with strangers is stupid.
He would not need a big boat, if he spends time on water then he surely knows others who have boats and maybe where to get one early in the morning without it being noticed.
Also Croes lives near the Shark feeding area and lives in Santa Cruz (F-9) and the shark area is near the Natural Bridge (C-9) which is almost a straight line up from Santa Cruz.
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