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COOPER (voice-over): A little girl lost.

KATE MCCANN, MOTHER OF MADELEINE MCCANN: We need our Madeleine. Our Madeleine needs us.

COOPER: Now reports of a breakthrough, and the authorities are talking to Madeleine McCann's mom. Is she a suspect? What do police know? The case on a case, with millions praying for a happy ending.

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COOPER (voice-over): It's May 3. A smiling girl sits by a pool. Her name is Madeleine McCann. This is the last photograph taken of the 3-year-old. She vanished just hours later.

KATE MCCANN, MOTHER OF MADELEINE MCCANN: We need our Madeleine. Sean and Amelie need Madeleine, and Madeleine needs us.

COOPER: The story has received international attention, catapulting Madeleine's parents into the world spotlight. There have been dozens of interviews, celebrity pleas, even a personal meeting with the pope.

Despite all the rumors and reports, one fact remains painfully clear: Madeleine is still missing.

Her story begins innocently enough, Kate and Gerry McCann, a British couple, take Madeleine and her twin 2-year-old brother and sister on vacation to a resort in Portugal.

UNIDENTIFIED MALE: Cheer up, Gerry. We're on holiday.

COOPER: On the evening of May 3, after the children were asleep, Kate and Gerry left their ground floor room and the kids alone to have dinner at a restaurant about 300 feet away. A short time later, Kate went to check on the kids and says she discovered Madeleine was gone. Gerry's relative describes what he told her.

UNIDENTIFIED MALE: He said that Madeleine had been abducted. She's not the type of wee girl to wander off. And they had been checking every half-an-hour on the children. The three children were sleeping in the one room. When Kate went back to check a half-an-hour after Gerry had checked, Madeleine was missing. The window was open. The shutters were open. None of that had been left like that.

COOPER: Local police are called. There's a search of the resort that is expanded to surrounding areas.

Within days, the McCanns make this heartbreaking public plea.

K. MCCANN: Please, please do not hurt her. Please don't scare her. Please tell us where to find her or put her in a place of safety, and let somebody know where she is. We beg you to let Madeleine come home.

COOPER: In the early stages of the investigation, place say Madeleine was kidnapped, but believed she was alive. By the second week, her image was broadcast around the world. A multimillion-dollar reward was offered.

Famous faces, like "Harry Potter" author J.K. Rowling and soccer star David Beckham, asked for help.

DAVID BECKHAM, PROFESSIONAL SOCCER PLAYER: If you have seen this little girl, please, could you go to your local authorities or police and give any information that you have, any genuine information that you have?

COOPER: Back in Portugal, the police pursued a number of possibilities. There were reports of Madeleine sightings and that a man was seen dragging a girl near the hotel.

There was speculation that Madeleine may have been taken by a child sex ring. At one point, authorities zeroed in on a British man staying at a nearby villa. He was questioned, the home searched, and then nothing.

In fact, none of the leads were verified. And the McCanns criticized authorities for mishandling the case. They also created this Web site, findmadeleine.

GERRY MCCANN, FATHER OF MADELEINE MCCANN: We would like to again thank the thousands, if not millions, of people who are doing little things in their own way.

COOPER: The McCanns traveled throughout Europe, holding press conferences. The flew to America to meet with missing children experts. On May 30, they had a personal audience with Pope Benedict XVI.

K. MCCANN: He said that he would pray for us and our family.

COOPER: Then, in early August, a potential major break: A newspaper says traces of blood were found on the wall of the room where Madeleine was staying.

G. MCCANN: Can't comment on any specifics and forensics. And we wouldn't do that.

COOPER: But the news was followed by words no one wanted to here.

OLEGARIO SOUSA, CHIEF INSPECTOR, PORTUGUESE POLICE: The little child could be dead. But we have not decided until this moment. We must wait for -- for the results from the lab.

COOPER: And, this week, Portuguese investigators are holding separate witness interviews with Gerry and Kate. Through a spokeswoman, the couple say they are happy to help police, and Kate believes her daughter is still alive.

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COOPER: For more now on those developments, let's go to CNN's Paula Hancocks, who is live in Portimao, Portugal.

Paula, what is the timeline here? Samples of blood found on the wall of the family's hotel room come back from being analyzed at this crime lab in Britain, and then, suddenly, Maddy's parents are brought in for questioning.

Is that just a coincidence?

PAULA HANCOCKS, CNN CORRESPONDENT: Well, Anderson, not particularly, according to everyone here on the ground. There's a real sense that something has changed, and that the circle of suspicion might be narrowing somewhat.

Now, we know that, less than 48 hours ago, they did, the Portuguese police, get some results from those forensic tests. They said they were satisfied with the results. And then they said to both Kate and Gerry McCann that they wanted to speak to them individually.

Now, we did see some extraordinary scene here just a few hours ago, quarter to 2:00 in the morning local time. We saw Kate McCann coming out of the police station behind me. She had been in there about 11 hours on her own, without her husband, talking to Portuguese police. She looked visibly drained by the experience.

Now, her lawyer did say that she is still a witness. She is not a suspect. But some members of her family are saying they're worried that the finger of suspicion is going to start pointing at the family itself now.

And, tomorrow, the husband, Gerry McCann, will have to go through exactly the same thing.

COOPER: How -- how reliable do authorities say that these forensics are?

I mean, the Portuguese police have made a bunch of mistakes in this case. They allowed the hotel room that they stayed in to be let out as soon as Maddy's parents moved out. They -- they did not impound their -- their rental car. At the very least, if -- if they suddenly do come under suspicion, there's a trial, I mean, a defense lawyer can poke holes in -- in the chain of evidence.

HANCOCKS: Well, that would certainly be a worry.

The forensics tests themselves were carried out in Britain, so there's no doubt surrounding those. And -- but it did take a couple of months before sniffer dogs came from Britain and actually discovered these traces of blood. There have been criticisms about the way that the Portuguese police have dealt with this particular case.

The very fact that they would rent out a crime scene and allow people to go into that room and rent it out after this had happened is quite staggering. And, certainly, the Portuguese media and the British media have been suggesting that many, many mistakes have been made. But the actual forensics tests themselves, those were done in Britain. And the Portuguese police say they're very satisfied with those.

COOPER: All right, Paula Hancocks on the scene.

We will bring you any developments as warranted.

Thanks very much.