The detectives said in a release posted on the Metropolitan Police Service's Web site a team of 37 investigators spent the past year reviewing the Portuguese inquiry into Madeleine's disappearance and have decided the case should be reopened. Portuguese authorities closed the case in 2008.
Scotland Yard also released an age-progression photograph of Madeleine whose ninth birthday is May 12. She was nearly 4 years old when she disappeared May 3, 2007. The enhance photo was done by a forensic artist who worked closely with her parents, Gerry and Kate McCann.
Detective Chief Inspector Andy Redwood said there are two possibilities:
"One is that Madeleine is still alive; and the second that she is sadly dead," he said.
"Based on the former we are releasing the age progression image today with a specific appeal. If you know where Madeleine McCann is now or you have new direct information/evidence about what has happened to her then please contact us."
He urged anyone who was at the Portuguese resort between April 28 and May 3, 2007, and has not spoken with police either in Portugal or in Britain to contact Scotland Yard.
Redwood said the team has identified 195 "investigative opportunities."
Officers are poring over about 40,000 pieces of information equating to about 100,000 pages, Scotland Yard said.