The search for Dr Ruja Ignatova takes an unexpected turn when a story emerges alleging she's been murdered. But with with sightings of Dr Ruja still coming in long after her apparent demise, can it be true? We speak to the Bulgarian journalists behind the story and team up with BBC colleagues to investigate the murder theory. It takes us on a trail to a Bulgarian man widely suspected of heading an organised crime organisation. Meanwhile, a trusted former adviser to Dr Ruja disappears, just like his old boss.

Presenter: Jamie Bartlett Producer: Rob Byrne Executive Producer: Georgia Catt Commissioner: Dylan Haskins Series Editor: Philip Sellars Original music and sound design: Phil Channell Original music and vocals: Dessislava Stefanova and the London Bulgarian Choir Featuring material from: LiveNow from Fox, Radio 100,7. The Missing Cryptoqueen is a BBC Studios Audio production for BBC Sounds and BBC 5Live

How mysterious friends in influential places may have helped Ruja stay one step ahead. A massive revelation we only now know, but which Ruja knew years earlier.

Who are they? And could they be helping her now?

CREDITS Presenter: Jamie Bartlett Producers: Rob Byrne and Georgia Catt Original music and sound design: Phil Channell Original music and vocals: Dessislava Stefanova and the London Bulgarian Choir Studio Engineer: Giles Aspen Series Editor: Philip Sellars Commissioner: Dylan Haskins The Missing Cryptoqueen is a BBC Documentaries production for BBC Sounds and BBC 5Live

The search for Dr Ruja Ignatova gathers pace, five years after she disappeared. Files leaked from Dubai reveal how Dr Ruja stashed millions in the emirate and struck up a relationship with a mysterious sheikh. Then, a careless selfie leads the podcast to a mansion in an exclusive gated community. As the FBI steps up its search, new information surfaces about Dr Ruja’s disappearance from an unlikely source.

Presenter: Jamie Bartlett Producers: Rob Byrne and Georgia Catt Series Producer: Georgia Catt Commissioner: Dylan Haskins Series Editor: Philip Sellars Original music and sound design: Phil Channell Original music and vocals: Dessislava Stefanova and the London Bulgarian Choir Featuring footage from: LiveNow from Fox, 5en News, Prag News, Welt Netzreporter The Missing Cryptoqueen is a BBC Documentaries production for BBC Sounds and BBC 5Live

The search for Dr Ruja is back on. A lot has happened since Episode 8.

Original music and sound design: Phil Channell Original Music and vocals: Dessislava Stefanova and the London Bulgarian Choir

This audio was updated on 12/08/2020 to reflect additional correspondence with Chelgate.

The final episode takes an unexpected twist.

Presenter: Jamie Bartlett Producer: Georgia Catt Additional Research: Ignatius Bahizi Editor: Philip Sellars Original music and sound design: Phil Channell Original Music and vocals: Dessislava Stefanova and the London Bulgarian Choir

Could Dr Ruja and the missing billions be hidden in plain sight? A number of small leads seem to be pointing to one place.

Presenter: Jamie Bartlett Producer: Georgia Catt Editor: Philip Sellars Original music and sound design: Phil Channell Original Music and vocals: Dessislava Stefanova and the London Bulgarian Choir

Episode 7 of 8. Released weekly

In 2009 Dr Ruja and her father bought a metallurgic factory in Southern Germany. What does this have to do with her disappearance today? Those who knew her at the time tell a strangely familiar story about the impressive businesswoman who came to save their workplace.

Presenter: Jamie Bartlett Producer: Georgia Catt Editor: Philip Sellars Original music and sound design: Phil Channell Original Music and vocals: Dessislava Stefanova and the London Bulgarian Choir

Episode 6 of 8. Released weekly.

'Who is to blame?'

One of the world's highest-earning Multi-Level-Marketers and former OneCoin top seller agrees to speak. In his mansion on the outskirts of Amsterdam, Jamie learns the secret behind OneCoin's rapid growth and the huge amounts of money that has been made by those at the top.

The Missing Cryptoqueen is an eight-part series for BBC Sounds, with new episodes every Thursday.

Presenter: Jamie Bartlett Producer: Georgia Catt Editor: Philip Sellars Original music and sound design: Phil Channell Original music and vocals: Dessislava Stefanova and the London Bulgarian Choir Written and researched by Jamie Bartlett and Georgia Catt

Jamie and Georgia arrive in Bucharest in the hope of seeing their first OneCoin event: The Miss OneLife 2019 Beauty Pageant. Who else could be there?

The Missing Cryptoqueen is an eight-part series for BBC Sounds, with new episodes every Thursday.

Presenter: Jamie Bartlett Producer: Georgia Catt Editor: Philip Sellars Original music and sound design: Phil Channell Original Music and vocals: Dessislava Stefanova and the London Bulgarian Choir Written and Researched by Jamie Bartlett and Georgia Catt

In Spring this year, something unexpected happened. On March 6th 2019, Dr Ruja's brother Konstantin was arrested at Los Angeles International Airport and charged with money laundering and fraud in connection with OneCoin. Dr Ruja was also charged in absentia, and US authorities declared OneCoin a fraud. We thought this could be the end of OneCoin, and our search. It wasn't. Why?

The Missing Cryptoqueen is an eight-part series for BBC Sounds, with new episodes every Thursday.

Presenter: Jamie Bartlett Producer: Georgia Catt Story Consultant: Chris Berube Editor: Philip Sellars Original music and sound design: Phil Channell Original music and vocals: Dessislava Stefanova and the London Bulgarian Choir

Not all is as it seems with Dr Ruja's revolutionary cryptocurrency, OneCoin.

The Missing Cryptoqueen is an eight-part series for BBC Sounds, with new episodes every Thursday.

Presenter: Jamie Bartlett Producer: Georgia Catt Story consultant: Chris Berube Editor: Philip Sellars Original music and sound design: Phil Channell Original music and vocals: Dessislava Stefanova and the London Bulgarian Choir