Two e-fits of a man who was seen carrying a child near where Madeleine McCann went missing have been released by police ahead of a new television appeal for information.
The images of a man with dark hair are based on descriptions from two witnesses who were staying in Praia da Luz, Portugal, when the little girl went missing on May 3, 2007.
Detectives now believe the sighting is much more significant than previously thought and one of the main priorities for the investigation is to identify the man.
The witnesses described him as white, aged between 20-40, with short brown hair, of medium build, medium height and clean-shaven.
Detective Chief Inspector Andy Redwood, the senior investigating officer, said that while this is far from being the only line of inquiry, it is of "vital importance".
"Whilst this man may or may not be the key to unlocking this investigation, tracing and speaking to him is of vital importance to us.
"We have witnesses placing him in the resort area around the time of Madeleine's disappearance.
"This is far from our only line of inquiry and there will be e-fits released of other sightings as well, who we are equally keen to trace. These people were seen on the day of Madeleine's disappearance and the days leading up to it," he said.
He added that detectives have been able to "make massive steps forward" by drawing together all the material gathered to date and reviewing it as a whole.
"We continue to put Madeleine at the heart of our investigation and I would urge people to watch Crimewatch tonight and if you can help identify this man or have any information about our new appeal points, please contact us.
"Praia da Luz is a popular holiday destination for many nationalities so our requests for help need to be repeated in many different countries. I will be travelling to Holland, Germany and Ireland to seek the support of the public there.
"If you were in and around the Praia da Luz resort on Thursday May 3 2007, but you have not yet spoken to police, and you think you may have information, please pass it on.
"I would also like to ask for the help of the local community in Praia da Luz. Portugal is a key country for us to trace any outstanding witnesses and our appeals will be repeated there.
"We still have a lot of material to investigate and much work to do. Your information could be the vital piece we need to finally answer what happened to Madeleine."
In a clip from tonight's Crimewatch, released by Scotland Yard, mother Kate McCann says: "We're not the ones that has done something wrong here. It's the person who's gone into that apartment and taken a little girl away from her family."