No sign of Madeleine McCann, 13 years on

Madeleine McCann should be celebrating her 17th birthday next week with parents Kate and Gerry. Instead, the couple will mark the occasion with a sombre vigil at the family's home in Leicestershire. They will leave birthday presents in her bedroom, alongside the ones they left for her 16th birthday, and which remain unopened 12 months on.

Yesterday marked the 13th anniversary since Madeleine went missing from a holiday apartment in the Portuguese resort of Praia da Luz, about 60 yards from where her parents were having a tapas meal with friends.

Gerry and Kate, who both worked as doctors, arrived at Mark Warner holiday complex in the Western Algarve on April 28, 2007, for a seven-day holiday with a group of friends. On May 3, the sixth night of the break, they left Madeleine, then nine days shy of her fourth birthday, in the bedroom she was sharing with her twin brother and sister, Sean and Amelie, aged two. They left the apartment at 8.30pm to join their seven friends for dinner at a restaurant across the pool from their flat. At 9.05pm Gerry went back to the apartment to check on the children, entering through a patio door he had left unlocked to avoid waking them. A few minutes later, he returned to the restaurant reporting that all was well. At about 9.30pm, Kate got up to check again, but friend Matt Oldfield said he was going to look in on his own children, and offered to check on the McCann children too.

At 10pm, Kate went to check on the children for the third time, and immediately became alarmed when she noticed the bedroom door swinging in the breeze. She quickly discovered window had been opened, and that Madeleine had vanished from her bed.

Recalling the moment he discovered Madeleine was missing, Gerry said "automation kicked in", and he began searching the apartment.

"Kate came running back from the apartment, Kate was screaming 'Madeleine's gone', and I said 'she can't be gone'," he said.

"I'm running in checking the bedroom, checking everywhere, even places I know she couldn't be, like under the kitchen sink and in cupboards.

Mr Oldfield's wife Rachael told friend Jane Tanner, who had also been dining with them, what had happened, and she replied that she had seen a man carrying a young girl.

Mr Oldfield went to the resort's 24-hour reception, and asked staff to contact police. He later admitted he only made a cursory check at the McCann's apartment, poking his head through the door and seeing the twins in their cot, and did not actually see whether Madeleine was in bed or not.

Local police arrived at 10.30pm, followed 40 minutes later by detectives who spent the next five hours searching the immediate vicinity, before calling off the hunt. They quickly noticed a latch lock on the sliding window; it was later discovered that cleaners often opened the windows to air the rooms, so there is no way of knowing whether the window was locked that night or not.

Madeleine's disappearance quickly sparked what became described as the most-reported missing persons case in history. Pictures of Madeleine, focusing on the distinctive mark in the iris of her right eye, were beamed across the world as an international search began.

On May 15, the McCanns set up a campaign fund to raise money and awareness. Over the first two days its website receive 58 million hits, and throughout May and June the McCann's PR team ensured that Madeleine would dominate the news headlines.

Early investigations focused on Miss Tanner's reported sighting of a man dressed in a dark jacket, beige trousers, and carrying a young girls at about 9.15pm on the night in question. Police interviewed British-Portuguese man Robert Murat, who lived nearby. On May 17 his home was thoroughly searched with the aid of sniffer dogs, and his pool drained, but no evidence was found against him and he was declared to no longer be a suspect.

British GP Dr Julian Totman – who, earlier in the day had been playing tennis with Gerry – said he believed he was the man Miss Tanner had seen that night, after he had picked up his daughter from the on-site creche.

In the early stages, the investigation was led by the Portuguese police, with support from the Leicestershire force. It soon became apparent that the two forces had very different approaches; while the British police filed information into a national computer database, while their Portuguese counterparts preferred to use traditional paper files. Tensions quickly emerged, with reports that the Portuguese force felt patronised by the British officers, who were accused of behaving like a colonial power.

Relations between the Portuguese police and the McCanns quickly soured, and on September 7, 2007, the couple were declared suspects in the investigation. Two days later, Chief Inspector Tavares de Almeida signed a nine-page report concluding that Madeleine had died in an accident, and that the McCanns concealed the body and faked the abduction. Kate McCann later said she was told that if she confessed to this version of events, she would receive just a two-year prison sentence, and that her husband would face no charges.

In July 2008, the Portuguese attorney general concluded there was no evidence against either the McCanns or Murat, and they were no longer considered suspects.

In 2009, the McCanns met with then home secretary Alan Johnson asking for a review of the case. A report found how a number of different British agencies were involved in the search for Madeleine, but with little in the way of co-ordination. The report also called for renewed co-operation with the Portuguese police.

Mr Johnson's successor, Theresa May, announced in May 2011 that Operation Grange, a new British inquiry, would be opened, working in partnership with the Portuguese police.

Det Chief Inspector Andy Redwood was appointed senior investigating officer, and made it known from the start that the operation was looking at a "criminal act by a stranger", most likely a planned abduction or a burglary that Madeleine had disturbed. It was revealed there had been a four-fold increase in burglaries in the vicinity between January and May 2007, with two in the McCann's block in the 17 days before Madeleine's disappearance. In both cases, the intruders entered through the windows.

Another theory is that Madeleine simply wandered off, and was either abducted outside the apartment, or fell into one of the construction sites nearby.

Speaking in 2013, Redwood said the disappearance looked like a pre-planned abduction, which "undoubtedly would have involved reconnaissance". In an interview marking the 10th anniversary of Madeleine's disappearance in 2017, Scotland Yard's Assistant Commissioner Mark Rowley appeared to think the burglary theory unlikely, although he did not discount it completely.

Thirteen years on, and despite £11.5 million having been spent by the Home Office on Operation Grange, it seems we are no wiser to Madeleine's whereabouts than on the night she went missing. Four people were identified as suspects in 2013, but no further action was taken. In February this year Carol Hickman, a 59-year-old British expat working as a barmaid in Praia da Luz, was questioned by the Metropolitan Police about her German ex-boyfriend Michael Jehle.

Gerry and Kate have pledged never to give up in the search for their daughter, although several experts have said the chances of finding her are remote.

As every year goes by, the chances of finding Madeleine alive begin to look slimmer. But it is a sobering thought that there could be a 17-year-old going about her business completely unaware that she is the most-sought person in the world.