Perhaps the problem in Aruba is that the suspect is behind bars. If he were free and under surveillance he might lead us to the body.
In my opinion, Natalee's body, for all practical purposes, no longer exists in any form that can be used for forensic purposes, perhaps including identifying. I've always thought they dumped her at sea using one of the party boats--if so, the sea quickly disposes of them. The best they might hope for would be if they could find some jewelry or something that the fish can't or won't eat. The rest would be gone.