In answer to Gromit's post, I think they were 48 perfectly reasonable questions, given that the first suspects in any child abduction case are usually the parents or immediate carers.
I do not think that the child's parents murdered her, neither do I believe they know where she is. What I do think is that, apart from leaving the kids unattended, they were up to something with their 'friends' that night that they'd rather wasn't public knowledge, and that all those 'friends' have very carefully worked out stories together to make one verifiable one.
I don't think this cover up was the direct cause of the child's disappearance, but I do think it's jeopardised the investigation. Sooner or later, someone's going to slip up, though, and the press will have another field day.