A new suspect has emerged in the investigation into the disappearance of Madeleine McCann.

The focus on him is the latest in a series of twists and turns in one of the most high-profile missing person cases in recent history, which saw the three-year-old disappear from a holiday apartment in the Portuguese resort Praia da Luz in 2007.

Among the inmates of Kiel's high-security jail in northern Germany, there is one prisoner who has become the most notorious of all.

He's isolated for his own protection and allowed to exercise, alone, for only one hour a day.

With the publication of his full name restricted under German privacy laws, he is only known as Christian B - but there can't be many who don't know exactly who he is.

He's German, aged 43, and what used to be called a drifter-flitting between Germany and Portugal for many years and working a variety of odd jobs when he wasn't committing crimes.

It's three months since the convicted paedophile, rapist and drug trafficker was identified as the latest suspect in the Madeleine McCann case, suspected of abducting and killing the little British girl who vanished 13 years ago during a family holiday in Portugal.

The case against him is circumstantial - he is a convicted paedophile, he lived in the area, and on the night she disappeared, his mobile phone was in use nearby.

The next day he changed the registration of one of his vehicles.

As investigators continue to search for the vital evidence they need to charge him with Madeleine's abduction, Christian B is now the subject of three new investigations in Portugal.

I've covered the Madeleine McCann mystery since she disappeared. Over the years I've reported on various suspects, all of them eventually ruled out, but I wanted to find out, have they got the right man this time?

The prosecutor versus the defense lawyer

I've travelled far and wide across Europe covering this case. The first stop on my latest journey is Braunschweig in central Germany to meet the man in charge of the investigation into the connection between Christian B and Madeleine.

Braunschweig prosecutor Hans Christian Wolters believes Madeleine is dead and Christian B killed her, though he won't reveal why he is so certain.

But three months after he launched a global public appeal for new, vital clues, he still hasn't got enough evidence to charge him.

At his office near the reconstructed medieval town centre, Mr Wolters said: "We have found nothing in the past three months to make us think we've got the wrong suspect, but the evidence we have now is the same we had when we made our first appeal on 3 June.

"We have had hundreds of calls - 400 to us and hundreds to Scotland Yard - but we haven't got the information we need to charge Christian B.

" But there are some clues that make us hopeful our investigation will be more successful," he added.

The German, British and Portuguese authorities have targeted Christian B for three years, since a criminal associate of his told police he had effectively confessed to him, in a bar conversation, that he had abducted Madeleine.

But they've been unable to find forensic evidence that links the suspect to the victim, even though they have examined the VW camper van and Jaguar car he was driving at the time.

Mr Wolters said: "There is no forensic evidence, but it is not necessary to have forensics to charge our suspect.

"We just need more evidence, but I can't say what it is we are looking for though there are different possibilities. Maybe a witness, a photo or a video."

He added: "Someone asked me if we had found Madeleine's clothes. If we had found something like that it would be great for our investigation, but it's not true."

The prosecutor described as "speculative" a recent two-day dig at Christian B's former home outside Hanover, saying: "We are checking everywhere he lived and we know from his past that he liked to bury things like the USB computer sticks that were found in a previous investigation.

"I can't tell you what we found."

Mr Wolters said the Portuguese police had searched some wells on information supplied by the Germans and there had been other searches that were not publicised.

The suspect is imprisoned 300km away in the port of Kiel, where he's nearing the end of a sentence for drug trafficking.

His lawyer Friedrich Fulscher insists the prosecutor is wrong and Christian B isn't the man who abducted Madeleine, though he hasn't been shown the evidence against him.

In his spacious office, 2km from the prison, Mr Fulscher said: "I don't know any more after three months because I can't look in the prosecutor's files.

"He still hasn't told us anything. It isn't fair for him to keep accusing Christian B of killing the girl without telling us the evidence he has.

"There is a legal principle, that both sides have to have the same weapons. It's time for the prosecutor to show his cards, because he is prejudging my client in public without giving him the chance to go into action."

He accused the prosecutor of turning the public against Christian B and is worried about the suspect's future if he is never charged over Madeleine.

Mr Fulscher said: "If he is not charged there will be no chance for him to lead a normal life anywhere in the world because everyone will connect him to the case.

"He should have the right to go back into society and be rehabilitated."