A prosecutor who believes Madeleine McCann was killed by a German sex offender says the public would reach the same conclusion if they “knew the evidence we had”.
Hans Christian Wolters told the BBC that while his team does not currently have enough evidence to charge Christian B, he is “very confident”.
Their prime suspect is in prison serving sentences in Germany for drug smuggling and rape.
Madeleine disappeared in 2007.
She was on holiday with her family in Praia da Luz, Portugal, at the time of her disappearance, the same resort where Christian B raped a 72-year-old American woman.
Suspects’ surnames are not usually revealed in Germany for privacy reasons.
Although Christian B, 43, was identified as a suspect in June prosecutors do not have enough evidence to charge him.
Mr Wolters said: “If you knew the evidence we had you would come to the same conclusion as I do but I can’t give you details because we don’t want the accused to know what we have on him – these are tactical considerations.”
The six-month investigation has yielded fresh evidence of other alleged crimes.
Christian B lived in Portugal on and off for years and investigators now believe he may have committed at least three other sex crimes here – two of them against children, Mr Wolters said.
He said charges may follow early next year.
Mr Wolters said progress in the case of Madeleine was slower because of the logistical challenges posed by a disappearance now 13 years old in a different country.
But he said his team was working to build a water tight case against him.
Christian B recently lost an appeal against his rape conviction and will remain in prison for a seven-year sentence once his current drugs sentence ends in January.
Mr Wolters said: “I can’t promise, I can’t guarantee that we have enough to bring a charge but I’m very confident because what we have so far doesn’t allow any other conclusion at all.”
Last week, Met Police commissioner Dame Cressida Dick said that the Met’s position had not changed since the summer, when the force said its investigation – Operation Grange – remained a missing person inquiry as there is no “definitive evidence whether Madeleine is alive or dead”.
Madeleine, from Rothley in Leicestershire, went missing from a holiday apartment in Praia da Luz, on 3 May 2007, shortly before her fourth birthday.
Christian B is currently serving a prison sentence for drug offences in Germany and lost an appeal last month against a further seven-year sentence for rape.
He attacked the American woman in 2005 in the same area where Madeleine disappeared about 18 months later.
Police believe he was regularly living in this part of Portugal between 1997 and 2007, staying in a camper van at the time he is suspected of abducting Madeleine.