I rewatched the pilot and in my opinion, Daniel is who is shot. It's someone in a white dinner jacket. Jack does find the body but the shooter was wearing gloves and Jack did not have gloves on. Of course, he COULD have taken them off. Emily was phoneing the victim so...did she do it? Emily had sand on her hands at the party. Also, when she was questioned as to Daniel's where abouts she knew he was "on the beach".