The Madeleine McCann case has created more questions than answers and left police baffled as to who was behind the 3-year-old girl's disappearance in 2007.
But one potential clue in mother Kate McCann's 2011 memoir has raised eyebrows.
In her memoir, titled Madeleine: Our daughter's disappearance and the continuing search for her, Kate makes specific mention of a note written in an apartment complex restaurant booking she only discovered a year after police files were released to the public.
In it, Kate describes her horror at discovering a note from the holiday apartment complex when she was combing through Portuguese police files.
In her book she writes: "It wasn't until a year later, when I was combing through the Portuguese police files, that I discovered the note."
Kate spent six months analysing the 5000 pages of police files that were released and describes the night she made the restaurant booking that would change their lives forever.
In her book, Kate explained the unusual events in how her booking at the tapas restaurant was documented.
The tapas restaurant was small and it proved complicated to accommodate the McCann's booking for nine.
The party of nine managed to get a block booking for 8.30pm "pencilled in" for the rest of the week "after having a word with the receptionist at the pool and tapas area".
But after sifting through police documents Kate had concerns over the note written in the restaurant book and how accessible the book was to not only staff but the public.
Kate writes: "The note requesting our block booking was written in a staff message book, which sat on a desk at the pool reception for most of the day.
"This book was by definition accessible to all staff and, albeit unintentionally, probably to guests and visitors, too."
But it was the specific detail in the note that left Kate uneasy. It detailed how the McCanns were leaving their children home alone in their apartments, which could have been read by anybody in the restaurant the day Maddie disappeared.
"To my horror, I saw that, no doubt in all innocence and simply to explain why she was bending the rules a bit, the receptionist had added the reason for our request: we wanted to eat close to our apartments as we were leaving our young children alone there and checking on them intermittently."
Kate detailed how the group of nine decided to do their own "child-checking service" when they were at the tapas restaurant for dinner, instead of either bringing them to dinner or requesting the apartment complex's own child service.
"We now bitterly regret it and will do so until the end of our days."
In 2017 police were interested in talking to a former employee at the resort that may have evidence that could solve the case.
Police were also keen to talk to former employee Euclides Monteiro, an immigrant who had been fired from the beach club for stealing from guests. However, officials never got the opportunity after he died in a tractor accident in 2009.
Earlier this week it has been reported police working on the McCann case are reportedly closing in on a new prime suspect.
Portuguese police are perusing a "new clue and suspect" after talks with British officers, according to a bombshell local media report.
The Correio da Manha newspaper claims local detectives are now "nearer to knowing what happened to Madeleine" after receiving a tip-off from a mystery foreign man who was in Algarve at the same time Maddie disappeared in 2007.
The alleged tip-off has since led Portuguese police and Scotland Yard to share key information on the investigation.
A source in Portugal told the Mirror: "The British were here recently, there were talks at the PJ office in the city.
"It's all very secret but then it always is with the Madeleine case. Only the police know who the suspect is."
The face-to-face meeting between British and Portuguese police is believed to be the first since the new suspect came to light.