If the theory is she fell and died behind the couch perhaps she was still sedated, meaning if she had tests done on her, they would have found it in her system and the McCann's would be in one hell of a lot of trouble. Hence hiding her was the "easiest and safest" option. If she was buried in the sand (I think the beach was an extremely short walk from the apartments and most of the Tapas 9 believe Gerry was gone for around 30 minutes) then her body would have been quite well preserved. It's possible they could have gone back with their new hire car, taken Gerry's holdall, dug her up, put her in the holdall and into the boot of the car without being noticed had they done it at night. Where they eventually buried her is a mystery. They could have moved her to another beach and dumped the holdall in the sea. I'm sure there is a number of places. It doesn't bear thinking about but desperate people do desperate things. They are only human, although what they did was far from human to us