Friends of Gerry and Kate McCann are to be re-interviewed in the UK, the chief of Portugal's judicial police has said.
Madeleine's parents returned home to Leicestershire in September
The interviews will be conducted using questions written by Portuguese police investigating the disappearance of their daughter Madeleine.
Alipio Ribeiro also told Spanish newspaper El Pais that the results of forensic tests could be of "definitive help" in explaining what happened.
The McCanns were dining with three couples when Madeleine vanished.
Nothing ruled out
Mr Ribeiro said detectives and a prosecutor were planning to travel to the UK.
They will not be allowed to interview the witnesses themselves, so have prepared lists of questions which are to be put by British detectives.
The BBC's Steve Kingstone says no precise date has been given for the interviews.
He said the police may wait for final results of tests being carried out by Britain's Forensic Science Service.
Mr Ribeiro did not rule out any line of inquiry, but said the theory that Madeleine was dead still had the most force.
He expressed confidence that, sooner or later, detectives would "get a result", our correspondent adds.
And Mr Ribeiro said DNA analysis of samples recovered from the McCanns' holiday apartment and hire car could offer "definitive help" in establishing what happened to Madeleine.
Gerry and Kate McCann have always denied any involvement in their daughter's disappearance.
And their friends have defended them publicly, while saying they would assist detectives in any way they could.
Madeleine's father Gerry McCann, a consultant cardiologist at Leicester's Glenfield Hospital, has not worked since Madeleine disappeared from the family's apartment in the Algarve on May 3, days before her fourth birthday.
The family's spokesman, Clarence Mitchell, said: "No final decision has been taken on his return.
"It's one area that's under general consideration. It is hoped that he would go back before Christmas, but whether it happens in the next week or next month still has to be decided."
The former chief of the Metropolitan Police, Lord Stevens, has said the McCanns are the victim of a "witch hunt" and that there was no chance they would ever be charged with murder in the UK.
He told the News of the World newspaper that the Portuguese police should have treated them as the prime suspects from the outset. He said:
"That police error has become their tragedy now, because if they had been properly investigated back then they may well have been cleared."