The accepted version of events surrounding the disappearance of Madeleine McCann has "significantly changed", detectives have said.
It comes as pictures of men seen in and around the Portuguese town of Praia da Luz at the time of the girl's disappearance will be released as part of a BBC Crimewatch appeal to identify them and eliminate innocent sightings.
A short clip has been released ahead of the broadcast showing a reconstructed scene of Madeleine's parents Kate and Gerry McCann playing tennis.
Madeleine, dressed in pink shorts, a light-pink T-shirt and pink hat, then runs across the court, clutching a batch of tennis balls.
A full reconstruction lasting 25 minutes will feature in the BBC programme, which airs tomorrow at 9pm on BBC One.
In another clip, the McCanns are asked how often they think of their daughter, who went missing when she was three years old on 3 May 2007 from a holiday apartment as her parents dined at a nearby tapas restaurant with friends.
Mr McCann says: "When it's a special occasion, when you should be your happiest and Madeleine's not there, that's when it really hits home.
"Obviously, Madeleine's birthday goes without saying."
Mrs McCann adds: "It's when you have big family occasions really. That's it isn't it? 'Family occasion' and you haven't got your complete family."
Ahead of the programme, the senior investigating officer, Detective Chief Inspector Andy Redwood, said: "The timeline we have now established has given new significance to sightings and movements of people in and around Praia da Luz at the time of Madeleine's disappearance.
"Our work to date has significantly changed the timeline and the accepted version of events that has been in the public domain to date.
"It has allowed us to work with Crimewatch to build the most detailed reconstruction as yet, and highlight very specific appeal points.
"I hope that when the public see our investigative strands drawn together within the overall context of that appeal, it will bring in new information that moves our investigation forward."
Crimewatch presenter Kirsty Young will speak to the McCanns live in the studio during the programme, while presenter Matthew Amroliwala has been to Praia da Luz to explore the new focus of the police investigation.
During the programme, Mr Redwood discusses how the police have approached the inquiry, saying: "Primarily what we sought to do from the beginning is try and draw everything back to zero if you like.
"Try and take everything back to the beginning and re-analyse and reassess everything, accepting nothing.
"The careful and critical analysis of the timeline has been absolutely key.
"Primarily, we're focused on the area between 8.30 and 10.
"We know at 8.30 that was the time Mr and Mrs McCann went down to the tapas area for their dinner and we know that around at 10pm that was when Mrs McCann found that Madeleine was missing."
An incident room will be staffed during tomorrow's appeal and the days that follow, when the appeal moves to Holland and Germany.
A dedicated call centre will also be opened at Hendon, in north-west London.
Mr Redwood and his team recently revealed a vast log of mobile phone traffic could be the key to finding out what happened to Madeleine.
Scotland Yard detectives, who have interviewed 442 people as part of their review-turned-investigation, hope to track down as many people present in the Portuguese town at the time.
Since launching its own investigation, 41 people of interest have been identified by the Metropolitan Police, including 15 UK nationals.
Detectives have issued 31 international letters of request to mostly European countries in relation to some of the persons of interest as well as accessing phone records.
A large but "manageable" list of phone numbers identified as being present in Praia da Luz - though not necessarily used to make phone calls - has been drawn up by detectives with a "significant" number unattributed to any named person.
The Portuguese investigation is officially closed but authorities there are backing the Scotland Yard inquiry and officers from both countries will work together in pursuing new leads.
The Metropolitan Police now has a team of six Portuguese detectives based in Faro, who are carrying out enquiries on its behalf.
The McCanns are currently suing former police chief Goncalo Amaral for libel over claims in the book The Truth Of The Lie.