If any parent, myself included, were asked to imagine the worst kind of living hell, it might well go something like this. First, their child disappears from a holiday hotel room. A police investigation fails to provide any leads whatsoever. Finally, they themselves are accused by police of killing their own child and disposing of the body.

That is, of course, what has happened to Kate and then Gerry McCann, who have been declared arguidos, or formal suspects, by the Portuguese police. Kate McCann's face, glimpsed in pictures, looked particularly drawn. A friend initially described her response to the development as "stunned and disappointed". I imagine that the exhausted Mrs McCann has now become almost numb to whatever freshly surreal barbs of horror life can throw at her: the fiercest, deepest anguish possible surely came in May, with the disappearance of her daughter.

The world has now become intensely familiar with images of Gerry and Kate McCann, trapped in their unchanging distress like insects in amber. They receive the coverage normally afforded to celebrities, yet the sole source of their uneasy fame is the cruel fact that their daughter is missing.

After her disappearance, one friend of the McCanns reported having seen a dark-haired man making off with a sleeping child in his arms, and there were endless "sightings" of the little blonde girl. There have been pleas, posters, prayers and a meeting with the Pope, and back from the unknown has come the most dreaded sound of all: silence.

Early on, the McCanns decided to use the media as a megaphone to broadcast their search for Madeleine to every shadowy corner of the world. But the mass media is more than a simple instrument of broadcast: it is a half-tame tiger that will permit people to ride for a while upon its back while it roars, but may also turn and maul them.

In the case of the McCanns, the effect of the media has been double-edged. The publicising of their plight generated an enormous wave of public sympathy, albeit one with an undercurrent of prurient fascination.

Many people debated fiercely whether they themselves would ever leave their small children alone in a hotel room while they dined nearby with friends, and some openly attacked the McCanns for having done so. There were whispers of disapproval, too, for aspects of their behaviour that were not judged "in keeping" with their grim situation: some onlookers clucked disapprovingly when Kate went jogging, or seemed too composed, or when Gerry lost his temper.

This type of criticism, particularly of Mrs McCann, has always infuriated me: it is as though our society is perpetually eager to unmask a cold-hearted Lady Macbeth lurking behind the gentler image of a mother, wife or girlfriend. There are echoes of the much harsher press treatment meted out to Joanne Lees after her boyfriend Peter Falconio was murdered in the outback by Bradley John Murdoch in 2001. At the time there were widespread suggestions in the media that Lees - who had managed to escape the attacker - was suspiciously composed, and overt accusations that she had killed Falconio herself. It only later emerged that Lees had been given Valium and, in any case, how precisely should one behave after fleeing a psychopath who has shot one's boyfriend?

A similar question, I think, applies to the McCanns: how exactly should one behave when one's child simply disappears? Pray to God, if you like, that none of Kate McCann's critics are ever compelled to find out.

The media campaign has had another unpredictable effect. It has stirred up national resentments, and inflamed the Portuguese newspapers to wild accusations against the McCanns. The flailing Portuguese police, stung by largely legitimate criticism of what has undoubtedly been a bungled investigation, have evidently grown desperate for a swift resolution. The unreliable whiff of the Salem witch-hunt is entering the process: the McCanns have now been ensnared in the curious Portuguese legal no-man's-land of the "arguido" - and what of that other, continuing "arguido", Robert Murat, whose life has effectively been destroyed by the accusation?

Week by week, the public, first appalled, has gradually grown accustomed to treating the McCanns' search as a kind of running drama. Yet drama craves momentum, and last week brought a plot twist which has led a nation of armchair Poirots avidly to debate times, places and possible motives.

I find myself incapable of believing that the McCanns had anything at all to do with the disappearance of their daughter. We must, of course, await the outcome of the investigation. But we would do well to remember that this is not in fact a Grimm's fairy tale, a soap opera, or a murder mystery. It is the real life of Kate and Gerry McCann, and it must now have become a place of agony beyond all understanding. Pity them, if you have any compassion at all, and demonstrate the minimum of grace: the ability to desist from judgment.