They know the drill. NO BODY, no crime (in most cases). My horrible guess is that they fed her to the sharks and we won't ever find her remains. They have nothing to gain by confessing and no one is going to rat fink on the other because they are all involved.
Too bad polygraphs aren't allowed in Aruba. Just darn.
The only reason for feeding her to the sharks would be if she were dead, or if she could ID them. Did they try to make money off her by selling her? Or did someone come along and take her from them?
If these guys saw her get nabbed and didn't do anything, then they are just as guilty because they are the ones that took her down there to begin with. jmo