Melanie McDonagh: Kate McCann is being tried in the court of celebrity

On 3 May, Kate McCann must have thought that there was no worse fate than to lose a child and not know what happened to her. She now knows there is a worse fate and it is to lose your child and to be accused of killing her.

In just over four months, Kate McCann has become a celebrity. The grim aspect of this very modern status is that it is as potent in the making of a villain as a victim. Her extraordinary photogenicity was once the means for promoting her campaign to find her daughter Madeleine; now it is a means to spread the case against her.

Mrs McCann was questioned for more than five hours on Friday; when she emerged, onlookers booed as well as cheered her. If she is indeed innocent – as I believe, pending further police evidence, she is – then the nightmarish aspect of her situation is that there is nothing she can say or do which will convince those who believe that there is no smoke without fire of her innocence.

If Gerry McCann's sister, Philomena, is correct in explaining the case put to Mrs McCann, the police believe that Kate killed Madeleine accidentally, possibly through an overdose of sedatives, and then hid the body, only to dispose of it 25 days later in a hired car. In other words, having seen her daughter die, she composedly found a hiding place for her little girl's corpse and went out with friends for a convivial dinner.

Then, at 10pm that night, she put on an extraordinary performance as a mother distraught at the loss of her daughter, a performance she sustained for four months in front of assorted global audiences from the press to the Pope. Finally, under the noses of waiting journalists, she and her husband got rid of the corpse. If true, Mrs McCann gravely mistook her vocation in becoming a doctor: she should have become an actor, or joined MI6.

Now the very factors which previously stood in her favour are working against her. So, she and Gerry McCann are doctors, respected professionals? That's good, no? Kelvin MacKenzie, the former editor of The Sun, recently wrote in his (brilliant) column that he believed in Kate McCann. He told the BBC yesterday that readers wrote back in their hundreds to declare that he was partisan because this was an educated middle-class couple and his reaction would have been different had the McCanns been black and working class. They're damned, then, for being respectable?

My husband is a medic and is not particularly sympathetic to Kate McCann, but he found it impossible to believe that two doctors could, given their training, have given a three-year-old child an overdose of sedatives – particularly administered with a syringe.

Of course, when there is foul play concerning a child, police are often justified in focusing on the family as well as on passing strangers. We are told the British police have been investigating the McCann's marriage and whether they lose their tempers easily; well, fair enough. Our sentimentality about the maternal bond is such that we are irrationally reluctant to believe that a mother could harm her own child.

But in the case of the McCanns there is no good reason for the natural reaction not to be the right one, that Kate McCann has first been left bereft and is now being wronged. For her, the real anguish is that the new focus on her as Madeleine's suspected killer will distract attention and publicity from the possibility that she desperately wants to be true – that her little daughter lives, and can still be found.