If you go by Amaral's version of events, Kate found Madeleine dead. He insists that because Eddie picked up certain items of her clothing.
Kate makes a gruesome discovery (the body of her loved and cherished daughter).
Gerry is oblivious and unaware in the restaurant.
Kate pulls herself together, returns to the restaurant, communicates traumatic news to Gerry (without anyone else noticing) and Gerry pulls himself together, exists the restaurant, returns to the apartment, scoops up the body of his daughter, whisks the body past the noses of Smiths, hides (Amaral's exact word) Madeleine's body on the beach, and returns to the restaurant.
Meanwhile Kate absences herself a second time from the restaurant and re-enters (before Gerry has even got down to the beach) to raise a fake alarm.
That is arrant nonsense.
The worse nonsense even Amaral himself rejects, before May 3rd.
For anything Amaral proposes to have the slightest chance of being right, there would have to be evidence of Kate and Gerry being simultaneously absent from the restaurant at some point between their joint arrival and Kate's alert.
There is none
Neither a plausible explanation of what might have happened to the remains of Madeleine between May 3rd and when the Renault was hired.