For most of us' the events in Portugal's Praia da Luz three summers ago are now a blur ? a distant unhappy memory of lighting candles' prayers and appeals for a little girl snatched from a holiday apartment.

But then something happens to remind us of Madeleine McCann and once again we catch our breath and try to imagine the misery her parents' Gerry and Kate' experience every day as another reminder of their missing daughter emerges in a child's laughter or a little girl's sudden captivating smile.

This will be their third Christmas without Madeleine and the maxim "time heals? could hardly be less fitting. If anything the ordeal of not knowing worsens with every bogus sighting and false claim. Yet still brave' strong and united they refuse to give up hope.

"If you know what has happened to Madeleine'? Kate and Gerry said this week' "its still not too late to do the right thing and come forward.?

There's no blueprint for how couples should manage an ongoing nightmare. The rule book on dealing with the pain of a missing child has yet to be written.

But at home' when twins Amelie and Sean are attending lessons at the school where Madeleine would have been their watchful big sister' Kate spends hours sifting through paperwork' searching for simple overlooked clues. When Gerry returns from work he joins her.

At one time I believed this need to scour every last detail might have been a ritual to assuage the guilt' real or imagined' any parent would feel over a child's disappearance.

But three years on it doesn't seem futile or pointless.

Children do' against all odds' reappear and might have done so earlier had every stone been turned or every minute detail properly examined.

A policewoman's hunch led to the discovery of Jaycee Lee Dugard a few months ago.

Snatched at the age of 11 from a bus stop in America's South Lake Tahoe we now know had there been more thorough searches of her captor's property her 18-year imprisonment in Phillip Garrido's filthy garden sheds may have ended sooner.

If anything has given succour to the McCanns it's the story of Jaycee Lee.

But its also helped persuade the cynics' who feel the couple have been pointlessly banging their heads against a brick wall' that they could be wrong.

And right now' as they face another difficult Christmas' the family need all our support.

The chilling reality is that someone knows what happened the night Madeleine disappeared. They understand the motive and the way her abduction was orchestrated.

It would be terrifying if' in our lifetime' despite all the advances of modern technology' high-speed communications and sophisticated policing skills' a three-year-old girl was able to disappear off the face of the Earth without a single human being's knowledge.

The McCanns have already backed a Europe-wide alert system for snatched children. Now the Child Exploitation and Online Protection Centre (CEOP) has gone further with a global campaign targeted at kidnappers and paedophile rings.

And for those of us who have pushed Madeleine to the furthest recesses of our memory we're reminded' thanks to age-processed pictures' of how she might look now.

For years America looked at similar photographs of Jaycee Lee Dugard and despaired.

She wasn't delivered back to her family by a miracle but by the sloppiness of an over-confident' arrogant criminal.

Everyone makes mistakes. And one day' the person responsible for Madeleine's disappearance will too.