It's been more than 15 years since Madeleine McCann disappeared from her holiday apartment in Portugal's Algarve, triggering a missing persons' case that has only heightened the anguish for her parents Gerry and Kate.
But a development this week could herald a major breakthrough after Portuguese police formally identified German national Christian Brueckner as a murder suspect.
Investigators have given convicted sex offender Brueckner, 44, the title of “arguido” — meaning he is now officially the centre of the criminal investigation.
Brueckner is currently serving a prison sentence in northern German for raping a woman in 2005.
Here is a breakdown of the main events since Madeleine, 3, vanished.
– May 3: Kate and Gerry McCann, from Rothley, Leicestershire, leave their children asleep in their holiday apartment in Praia da Luz in southern Portugal, while they dine with friends at a nearby tapas restaurant.
Nothing is amiss when Mr McCann checks on the youngsters just after 9pm, but when Ms McCann goes back at about 10pm she finds Madeleine missing.
Jane Tanner, one of the friends dining with the McCanns, reports having seen a man carrying a child earlier that night.
– May 14: Detectives take Anglo-Portuguese property developer Robert Murat in for questioning and make him a formal suspect — but this is later withdrawn.
– August 11: Exactly 100 days after Madeleine disappeared, investigating officers publicly say for the first time that she could be dead.
– September 7: During questioning of Mr and Mrs McCann, detectives make them arguidos in their daughter’s disappearance — but this is also later withdrawn.
– September 9: The McCanns, with their twins Sean and Amelie, 2, fly back to England.
– July 21: The Portuguese authorities shelve their investigation and lift the arguido status of the McCanns and Robert Murat.
– May 12: Mrs McCann publishes a book about her daughter’s disappearance, on Madeleine’s 8th birthday.
London's Metropolitan Police launch a review of the case after a request from Theresa May, home secretary at the time, supported by David Cameron, prime minister at the time.
– April 25: UK detectives say they believe Madeleine could still be alive, release an age-progression picture of how she might look at 9 and call on the Portuguese authorities to reopen the case. However, Portuguese police say they have found no new evidence.
– July 4: UK police say they have launched their own investigation ― Operation Grange ― into Madeleine’s disappearance, two years into a review of the case. They claim to have “genuinely new” lines of inquiry and have identified 38 people of interest, including 12 Britons.
– October 24: Portuguese police confirm that a review of their original investigation has uncovered new lines of inquiry, and they reopen the case.
– January 29: British detectives fly to Portugal, amid rumours they are planning to make arrests.
– June 3: Sniffer dogs and specialist teams are used to search an area of scrubland close to where Madeleine went missing.
– December 12: Detectives begin questioning 11 people who it is thought may have information on the case.
– September 16: The UK government says that the investigation into the disappearance of Madeleine has cost more than £10 million.
– October 28: London's Met Police cuts the number of officers working on the inquiry from 29 to four.
– April 30: The McCanns prepare to mark 10 years since their daughter’s disappearance with a BBC interview in which they vow to do “whatever it takes for as long as it takes” to find her.
– May 3: Local media reports say Portuguese detectives are investigating a foreign paedophile as a suspect in the abduction of Madeleine.
– June 3: Police say a German prisoner — later named as Christian Brueckner, 43 — has been identified as a suspect in Madeleine’s disappearance.
– June 4: London's Met Police say Operation Grange — which had received £12.3 million in funding up to April 2020 — is still a missing person inquiry, as detectives have no “definitive evidence whether Madeleine is alive or dead”.
– May 4: Kate and Gerry McCann post a statement on the Official Find Madeleine Campaign website saying they still cling to the hope of seeing their daughter again, as they prepare to mark her 18th birthday on May 12.
– April 21: Christian Brueckner is made an arguido formal suspect by Portuguese authorities.