With other leads going nowhere, no wonder the parents are under suspicion, says william langley

A sweep of a suspect's garden produces nothing; a DNA test on a drink bottle from a Belgian restaurant turns out to be a dead end; a 98-day worldwide investigation has led nowhere. Which leaves only one possible explanation, one might think: the parents must have done it.

The denial has been swift: "'We didn't kill our daughter,' say the McCanns." (Daily Mail)

"Madeleine's parents deny suspicions." (Daily Telegraph)

It hasn't taken us long to get here. Around the McCann case now swirls a volatile mixture of extreme media expectancy and growing public cynicism. Within it lies not just the fate of a missing four-year-old girl, but a cautionary tale about the celebritisation of tragedy.

That Kate and Gerry McCann, as shining an example of middle-class wholesomeness as you could find anywhere, are now confronted by the implication they killed their own child could, regrettably, be seen as a consequence of the strategy they chose to pursue.

It is easy to second guess; to say that the McCanns should have taken themselves away with their anguish, and left what could be left to the police. Child abductions happen with depressing frequency. There were around 70 in Britain alone last year. None has ever exploded into the kind of global phenomenon represented by the McCann case.

Let's first consider how it happened.

The roots lie in both chance and design, and, to an understandable degree, naivete. One of the first calls a distraught Kate McCann made early on the morning of May 4 was to Jill Renwick, a family friend. Jill - unsure how best to help - called a London breakfast TV show asking how to get more information. Within minutes the bare bones of the story were on the air, and within hours, on a quiet news morning, it was being picked up everywhere.

The next trigger was the arrival in Praia de Luz, the Portuguese resort where the McCanns were holidaying, of veteran PR man, Alex Woodfall, a paid adviser to Warners, the holiday company.

Woodfall noted the parents' concern that the Portuguese police appeared reluctant to release information to journalists. "They feared that it would be a one-day story," he remembers. "They felt that if they could get Maddy's name and face into the media there was a better chance of her being found."

On one level their strategy has been wildly successful. Madeleine's angelic, wide-eyed face has become an international emblem of reproach. There are plans for a global 'Madeleine Day' during which world leaders, including former US President Bill Clinton, popular children's figures such as author JK Rowling, and celebrities like Sir Elton John will appeal for Maddy's return.

High-profile businesspeople, including Virgin tycoon Richard Branson, and the British retailing billionaire Sir Philip Green have boosted a reward fund now standing at more than £2.5m. The findmadeline.com website, featuring a daily blog by Gerry, has become one of the world's most visited.

What the McCanns could not have known was that the media spotlight and the public mood that it responds to is an unforgiving place. If the early coverage was a predictable mixture of genuine concern and gush, it wasn't long before awkward questions were being asked. Why did the couple leave Madeleine in their apartment? How come they seemed so collected? Didn't they seem to like the cameras rather too much? And finally... could they have done it themselves?

Now there are bloodstains, found in the apartment, to be examined. A breakthrough or another dead end? For the beleaguered McCanns, their every move under scrutiny, it may all amount to the same thing.