Almost two years after German prosecutors sensationally named him a prime suspect, Christian Brueckner is now an arguido, a formal suspect.
The million-dollar question is: what happens next?
Will Brueckner be formally charged over Madeleine McCann's disappearance, triggering a criminal trial that would surely draw the same intense media interest and public fascination as the court proceedings involving OJ Simpson or Michael Jackson?
READ MORE: Suspect 'worked at resort' where Maddie McCann vanished
Or will this arguido status simply linger over Brueckner's head for an indeterminable length of time, with prosecutors never charging him?
Both outcomes are on the table.
Currently locked up in a German prison for raping an elderly woman in Portugal, the arguido status could see Brueckner extradited to Portugal for questioning by the Policia Judiciaria (PJ), who are still investigating the 2007 mystery.
The prosecutor's office in Germany, who have driven the investigation into Brueckner over the past two years, appear to have a circumstantial case.
Prosecutor Hans Christian Wolters has repeatedly claimed to have "concrete evidence" Madeleine is dead and that Brueckner was responsible for killing her.
Brueckner has denied any involvement in Madeleine's unusual disappearance, when she vanished from her family's rented apartment in the resort town of Praia da Luz.
READ MORE: Madeleine McCann suspect injured while in custody
The initial Portuguese investigation ran from May 2007 to July 2008, and Brueckner is now the fourth person to be declared an arguido in the case.
The first was British man Robert Murat, named an arguido just 12 days after the three-year-old toddler mysteriously vanished on the night of May 3.
Arguido status hovered over Mr Murat for more than one year, until the case was closed by the PJ in July 2008 through lack of evidence.
Mr Murat was never charged in that time and he insisted he did not abduct Maddie.
Madeleine's parents, Kate and Gerry McCann, were also at one time declared arguidos.
Their arguidos status lingered for 10 months, and lifted when the case was closed.
Like Mr Murat, the McCanns were never charged and they too always denied any involvement in their daughter's disappearance.
If Brueckner is charged, he will fight those charges in court, according to previous conversations 9News.com.au has had with Brueckner's legal team.
A plea of not guilty from Brueckner would trigger a trial and a tidal wave of media coverage.
Any trial would likely see Mr and Mrs McCann and the Tapas 7, the group of doctor friends who holidayed with the McCanns in 2007, called to the stand as witnesses.
Media attention would be intense, given the circumstances Madeleine vanished.
The group said they were leaving their small children and babies alone in their holiday apartments at night while the adults ate dinner at a nearby tapas restaurant.
During the PJ investigation, there were questions over how an intruder could have broken into the apartment and a specialist cadaver dog team alerted inside the apartment the McCanns were staying and a hire car the family had rented.
For Brueckner to be charged, prosecutors will need to have sufficient evidence to be confident of winning.
Brueckner's legal team have complained a fair trial for their client is impossible.
For two years, German prosecutor Mr Wolters said his office did not yet have enough evidence to charge Brueckner, while insisting he was certain of the case against him.
Has that now changed?
It's possible German investigators have now built a strong enough case for charges to follow, in what would be a monumental development in this 15-year mystery.
Or, as Brueckner's legal team has claimed, was Brueckner named an arguido because Portugal's 15-year statute of limitations will expire in just over one week, on May 3.
If so, declaring Brueckner an arguido could be a judicial procedural play to ensure the case remains alive.
In an interview three years ago for true crime podcast Maddie, the lead Portuguese detective who worked the case, Goncalo Amaral, made the remarkable claim that a German pedophile he refused to identify would be made a "scapegoat" in the case.
British police were "preparing the end of the investigation, with a German pedophile who is in prison right now," Mr Amaral said.
Brueckner, a drifter with a criminal past of sex crimes and break in robberies, lived on the Algarve and in the coastal town Praia da Luz at the time Maddie went missing.
Mr Amaral was thrown off the case several weeks after Mr and Mrs McCann were named arguidos.
The detective claimed he was the victim of external political pressure on the PJ and he wrote a book in 2008 outlining his theory of what happened to Madeleine.
The 22-chapter work suggested an unproven theory that Madeleine had died in apartment 5A, an abduction was simulated and her body was somehow removed from the resort.
That book, The Truth of the Lie, started a bitter, years-long legal fight between Mr Amaral and the McCanns.
Over the weekend Mr and Mrs McCann said they "welcome the news" about Brueckner, and they hold out hope Maddie is still alive.
LISTEN: True crime podcast investigates what happened to Madeleine McCann
READ MORE: Three questions could help answer what happened to Maddie
"This reflects progress in the investigation, being conducted by the Portuguese, German and British authorities," they wrote in a statement.
"We are kept informed of developments by the [London] Metropolitan Police.
"Even though the possibility may be slim, we have not given up hope that Madeleine is still alive and we will be reunited with her."
German investigators are adamant the case is a homicide inquiry.
London's Metropolitan Police maintain they are investigating a missing person case.
Last month, it was reported the long-running, multi-million-dollar Metropolitan Police operation to find out what happened to Madeleine was on the brink of shutting down.
Launched in 2011 to review and investigate Madeleine's disappearance, Operation Grange has cost taxpayers $23.4 million.
"There are currently no plans to take the inquiry further," a source told British tabloid The Sun.
"The end of the road for Operation Grange is now in sight (and) the team's work is expected to be completed by autumn."
When contacted by 9news.com.au in March, London Metropolitan Police said "the investigation is ongoing".
Operation Grange has over the years conducted extensive searches around Praia da Luz.
Divers have descended into ancient wells, land has been excavated and old farm buildings and ruins searched.
No clues indicating what happened to Madeleine were found on those searches.
