Two years after Madeleine McCann vanished, the world is hardly any closer to learning the truth about what happened to her on the night of May 3 2007.

Despite a massive police investigation that spanned the globe and huge media and public interest, the fate of the little girl who disappeared while on holiday with her family in the Algarve remains unknown.

Even the release of thousands of pages of witness statements and expert reports from the official Portuguese case files last August served only to deepen the mystery.

Prosecutors in Portugal ruled last July there was not enough evidence to bring criminal charges against anyone and shelved the inquiry.

They noted the investigation achieved "very little in terms of conclusive results", including establishing for certain whether Madeleine was alive or dead.

Madeleine's parents, Gerry and Kate McCann, treat this lack of concrete evidence positively and insist they have not given up hope of finding their daughter alive.

They say they take strength from cases like that of Natascha Kampusch, the Austrian woman who was kidnapped aged 10 and held hostage for eight years before escaping in 2006.

The couple are aiming to capitalise on the renewed public interest around the second anniversary of Madeleine's disappearance to make fresh appeals for information that could help find their daughter.

While the Portuguese authorities are no longer actively investigating the case, the McCanns have a small team of retired senior British police officers working for them.

The couple had the investigative files translated into English and painstakingly went through them looking for clues that might have been overlooked.

So far Mr and Mrs McCann have kept quiet about any possible new leads from the documents, but they will reveal some of them in a Channel 4 documentary to be broadcast on May 7.

They are also using a high-profile television appearance in the US on the Oprah Winfrey Show to publicise new computer-aged pictures of how Madeleine may look now.

The past 12 months have been frustrating for the McCanns, from Rothley, Leicestershire, as time passes without any firm news of their daughter.

Their two younger children, twins Sean and Amelie, are now older than Madeleine was when she went missing from her family's holiday flat in the seaside resort of Praia da Luz.

The couple were relieved when prosecutors announced in July that they were no longer "arguidos", or formal suspects, in the case.

But this was tempered by frustration that detectives were no longer actively investigating what had happened to the missing girl.

They also faced fresh allegations by Goncalo Amaral, the one-time head of the Portuguese police inquiry into Madeleine's disappearance.

Three days after the case was shelved, he published a book in Portugal called The Truth Of The Lie, in which he alleged the young girl had died in her family's apartment on May 3 2007.

Mr McCann, 40, is continuing his job as a consultant cardiologist at Leicester's Glenfield Hospital but Mrs McCann, 41, has not returned to her work as a GP.

As well as working with their own detectives on the search for Madeleine, the couple have also lobbied MEPs for a Europe-wide missing child alert system.

Meanwhile, many people in Praia da Luz have grown fed up of their unwanted association with Madeleine's disappearance as they feel it has put off holidaymakers and damaged their livelihoods.

Mr McCann was barracked by a small number of locals when he returned to the village at the start of April to assist the filming of a reconstruction for the new Channel 4 documentary.

As the McCanns mark the sad anniversary of their daughter's disappearance, to be followed by her sixth birthday nine days later, there are still many unanswered questions.

It remains to be seen whether the next 12 months will bring any more answers.