Those who said they saw suspect Robert Murat outside the family's holiday apartment on the night she vanished may have named the wrong man, it was revealed.
Detectives believe the witnesses who said they saw the British expat could have confused him with a friend of Kate and Gerry McCann, David Payne, who was out searching for the missing three-year-old.
If true, the claim could force police into a rethink of their eight-month investigation.
Mr Murat, 34, has insisted he spent the night of May 3 at home in the villa he shares with his mother Jennifer, 72, less than 100 yards from the McCanns' holiday apartment in Praia da Luz, Portugal. His mother said he never left the house.
But a series of witnesses have given statements claiming to have seen him around the Ocean Club apartment complex in the hours after Mrs McCann, 39, raised the alarm.
They include three friends of the McCanns - Russell O'Brien, Fiona Payne and Rachael Oldfield - who later confronted Mr Murat at a police station after he was made a suspect and said he offered to help them search that night.