There's a slight, if noticeable, change in emphasis in the latest appeal to find Madeleine McCann.

It's not just the new artist's impressions showing how a six-year-old Madeleine might now look – a look that, according to yesterday's newspaper reports, shocked even her mother, Kate.

It's the message. It's a message aimed not at the child's alleged abductor but his confidante; the friend, the neighbour, the accomplice – someone who may have known something two-and-a-half years ago when Madeleine first disappeared, and has lived with that gnawing guilt ever since.

In the latest message, police are taking a well-aimed shot at that guilty conscience and hoping to burst it.

It's a short film but the words are carefully chosen, its purpose abundantly clear: Do the right thing. Come forward. Tell the police what you know.

Whoever you are, it's not too late to make things right.

It comes as Kate and Gerry McCann revealed yesterday that their four-year-old twins, Sean and Amelie, wanted to find and fight the person who took Madeleine.

The twins were just two when Madeleine vanished but they talk about their older sister a lot, said Gerry.

"Now they are saying, 'She's been taken, when we find who took her, we'll fight them'. That doesn't come directly from us saying that. Amelie said this week: 'When I find that man I'm going to do this and that'.

"I said, 'No, what we will do is we will give them to the police and then we'll put them in jail'.''

Mrs McCann, who has not returned to her post as a GP since Madeleine disappeared, said looking for her daughter had become a full-time job.

"I'm probably busier than I've ever been," she said.

The minute-long film was made by CEOP, the Child Exploitation and Online Protection police unit, which specialises in protecting children from abuse.

Jim Gamble is the man in charge of the unit.

"It's true that we are doing here is slightly different to what we have done in the past," he told the Mercury. "But also, we are conscious that it's two-and-a-half years further on, and we don't want to repeat what has been done so far."

Madeleine disappeared on Thursday evening, May 3, 2007, while on holiday with her parents in the sleepy Portuguese fishing town of Praia da Luz.

It was, for the summer of 2007 and much of that autumn and winter, the biggest story in the world.

From a police point of view, not much has happened since then. There have been no positive sightings of Madeleine since the day she vanished.

"This is about reflecting where we are now," said Mr Gamble.

"Although Madeleine is still missing, this is us acknowledging that things have changed. Human relationships change. Are you still friends with the people you were friends with two and a half years ago? Possibly not.

"Peoples' circumstances change. This appeal is not just about tapping the shoulder of the person who may have taken Madeleine and saying: 'We are still here, we are still looking' but it's also about their friend, their accomplice."

Would someone who committed the highest-profile crime of the 21st century really have confessed to someone else? Mr Gamble is sure that they would. "We have spoken to some of the best psychologists in the business," he said. "They are certain that someone else would know about this."

Temporary Chief Constable Chris Eyre, from Leicestershire Constabulary, said: "In May 2007, an innocent little girl went missing," he said. "We hope through this initiative someone will come forward and provide that information that will enable her to be found."

Every word in the minute-long message was pored over, says Jim Gamble, every word chosen for maximum effect – not necessarily for the millions of people around the world who will see it, but for the one person who doesn't want you to.

"It is just a short film, but we want people to see it," said Mr Gamble. "We want to push it up the internet charts ."

Not just to resurrect the profile of the investigation, but as a direct challenge to the man and his associate who are still out there, wishing all this would go away.

"Quite simply," says Mr Gamble, "this is their chance for redemption. Whoever you are and whatever you know, do the right thing. It is not too late."

You can see the minute-long film – you can see it at

ceop.police.uk/madeleine/madeleine.asp