If, as seems increasingly likely, the McCanns did kill their daughter (sleeping tablets?), how did they find the strength to lie to so many people in such a forthright unashamed way?....
They easily fooled the Pope, David Beckham, the British media, and hence the British public (though not the German media). They were accomplished at continuing their ruse and popularity even when the facts pointed to them being dodgy parents at the least (who leaves a 3 year old alone in an unlocked flat for an entire evening while on holiday?)
So successful have the McCanns been that, as Tygerland points out, even reasonable requests at questioning their behaviour is batted away as heresy (just like we fail to hold religion in general to account).
Did their (very public) religious belief help them in their need to lie, or worse is their religious belief just a sham to help bolster their public image? - something they have probably used many times (as many charlatans do) to great effect throughout their life to increase their status and fool those around them.
Their middle class occupational status certainly helped them to avoid scrutiny and suspicion, perhaps as much as their religion.
New Scientist has recently explored the evidence on morality and religion. Its conclusions are that church going intrinsic religious people (those who truly do believe there 'might' be a god and attend church as an end in itself) are more likely to be moral than the average, also are more likely to give to charity, help others etc. Those however, who are church going extrinsic religious people (who attend Church for social reasons or to improve their status in society) are not surprisingly, less likely to help others and are less moral than the average. The data unfortunately did not compare directly with openly atheist people (whom I suspect would also be more moral than the average). I would also have liked to have seen the data on what proportion of church goers are intrinsic and extrinsic and how was this decided. What category I wonder are the McCanns to be placed in?