I think that the people who claim the McCanns'/their friends' stories 'don't add up' are being naive. A brief stint on a jury/reading police witness statements/even reading biographies or even, God help us, 'true crime' books will show how incredibly oddly people act under pressure/in panic, in real life situations. I'm a novelist, and you couldn't have characters behaving the way real people do in a novel, because no one would believe it -- it wouldn't be 'credible' or 'in character' or 'flow', and no one would suspend their disbelief. Real life involves coincidences, chance, bad luck, random behaviour, misremembering etc etc in a way that fiction can't.
I sometimes think people are reading the Madeleine McCann case as fiction, and are quibbling and pointing fingers because it doesn't 'work' as a story. If a novelist was trying to establish a character as Definitely Good and Relatable, she wouldn't have them putting their children in a creche a lot on a family holiday, or leaving them alone to eat out with friends every night, or use Gerry McCann's somewhat impersonal language about his daughter's disappearance, or (as reported by the tabloids - I have no idea whether this is true or not) go jogging/play tennis within a few days of their daughter vanishing. You might have the villain of a novel do that, to 'prove' their lack of humanity.
But this is real life. People aren't good characters or villains. Decent, ordinary people aren't necessarily 'nice'. They don't necessarily act consistently, represent themselves well when they speak, do the things 'we' imagine we would do.
And unfortunately, there aren't always endings.