Do we know for sure who were the last people to see Maddie alive other than the parents, and what time was that?
If the McCanns did it, both or either, which God forbid, it would have had to have been BEFORE they sat down for dinner, to allow for the body to have been hidden already. They couldn't have risked a search of the apartment being made the moment she was found to be missing. So I'd say a lot depends on what happened between Maddie last being seen in public, and the McCanns sitting down for dinner.
No-one seems to have considered the possibility that - as in Belgium - there might be a paedophile ring existing in the locality, as was indeed reported at the start of all this; and that this ring involved people in positions of power. I think the police have developed a loathing of the McCanns for various reasons both public and personal, and would have a lot of incentive to fit them up, inc for reasons of 'national pride' I don't think from everything I've read that the forensic evidence is in the least to be trusted, given the sloppy procedures which have been used. It's becoming horribly possible that the McCanns will never be able to clear their names, if innocent, since the physical evidence will always be open to [mis]interpretation.