My take is that we were supposed to think the crime took place on the beach. It was a wild goose chase. Occams razor is that the perp committed the crime at his private apt. It's the simplest answer.
But even if it did take place elsewhere, why is it so difficult to understand that tossing a body into the deep ocean in Aruba is so difficult? That would be easy to do.
That's true, and I thought the beach was most likely because "wanna go to the beach" seemed very likely. However, if we call that a red herring, an after party "wanna go for a boat ride" also seems very tempting. It still really surprises me that she would do anything without telling somebody from the group though.