The fridge thing also wouldn't work because they were on holiday in a resort for less than that time, and cleaners would have spotted something straight away. The police would have done a forensics examination of the hotel room as well, as has been reported. They made the missing persons report almost straight away and any potential car hire would have been scrutinized by the police including forensics examination.
Whoever did the kidnapping knew what they were doing. The parents have no clue how they would kill a little girl and get away with it, they just don't have the know-how, the background, nor the motivation to. They had no debt. They enjoyed their holidays and their Christmases together. Both careers were flourishing. They loved their little girls.