In the interest of justice and fairness, innocent until proven guilty and all that, I will consider for a moment that Madeleine was snatched to order by an elite paedophile ring, (an accident waiting to happen) and the parents are not guilty of anything other than gross stupidity. If this was the case there would be no evidence of abduction because it would be covered-up at the highest levels, to protect politicians and police. Potential witnesses can be intimidated, or worse. The McCanns would be an easy target to implicate due to their hedonistic lifestyle. They were then manipulated by rich and powerful people. If spooks had access to the body they could plant forensic materials.
The trouble with this theory is it would require everyone from the PJ in Portugal to the FSS in Birmingham to collaborate. It would then be imperative for the British establishment and media to put the McCanns firmly in the frame and make them hate figures. That would have been easy enough to do, the public already treat them with contempt (see Mirror Forums) when they have been painted as pure as the driven snow, imagine the vilification if their names had been dragged through the mud! But the reverse is true... the press publish fairy stories to exonerate them. If they were to be stitched up, why did it take the CID so long to make them formal suspects?
Of course, none of this explains the McCanns bizarre behaviour in the absence of their daughter. If you want one specific irregularity, consider the fact that neither of them has ever addressed their missing child directly through the media. Apparently the FBI treats this as an indication of the parents guilt. On one occasion, when prompted by a reporter, who asked what would you say to Madeleine if she was listening? Kate said, Only that we love you, but she already knows that. She didnt look into the camera, choke-up, or break-down, in what should have been a gut-wrenching moment. As much as I would like to give them the benefit of the doubt, their actions betray them.