An FBI wanted former spy who served as the "Missing Cryptoqueen's" trusted advisor has vanished.
Frank Schneider, 53, was detained in France while under house arrest pending extradition to the US.
But like his former boss Ruja Ignatova, he vanished before being brought before a US court.
On charges of fraud and money laundering for his alleged involvement in a $4 billion (£3 point 2 billion) cryptocurrency scam, he could spend up to 40 years in prison.
The BBC received confirmation from French authorities that Mr. Schneider, who was wearing an ankle tag, had eluded his electronic monitoring.
On May 16, Nancy's Court of Appeal issued a new warrant for his arrest, making it clear that his whereabouts have been a mystery for more than a month. .
The BBC was unable to reach Mr. Schneider, his wife, or his attorneys.
He was a troubleshooter for Miss Ignatova, the mastermind behind the OneCoin cryptocurrency fraud. She boarded a Ryanair flight in 2017 from Sofia to Athens as investigators closed in on her, never to be seen again. A $500,000 (£400,000) reward is being offered by the FBI for information that results in her capture.
In August 2022, while under house arrest, Mr. Schneider told the BBC that he didn't think he would receive a fair trial in the US.
He admitted as much on the podcast The Missing Cryptoqueen, "I fear that I do not have access to a legal system in which I can properly defend myself.".
The system is heavily based on 'plea bargaining,' as they say. Now, that presents a problem for me because I fervently believe I am innocent.
"For a defendant, a trial in the US is a phenomenally expensive thing. Millions of dollars will be spent; in my case, between five and eight million. Those are sums that I do not possess.
Therefore, I'm not sure what would happen in the United States if I arrived there. ".
In April 2021, Mr. Schneider was first detained by French police as he was traveling with his family close to the border with Luxembourg. He was imprisoned for seven months before being released on house arrest.
He conducted a number of interviews with journalists from his home in a sleepy French village as he worked with attorneys to oppose his extradition.
Prior to founding Sandstone, Mr. Schneider, a Luxembourgese national, served as the director of operations for the nation's intelligence service.
He coordinated the London-based attorneys and public relations specialists who assisted the "Cryptoqueen" in extending her scam.
He is also accused by US prosecutors of giving her secret police information. Although he has refuted this assertion, he did give the BBC access to secret police documents that he claimed she had obtained from meetings with Europol. They seemed to demonstrate how, prior to going missing, she managed to elude the authorities.
The BBC re-interviewed Mr. Schneider in December 2022 for an upcoming podcast episode and movie. He denied claims that he had ever considered evading extradition despite losing an appeal two months earlier.
Runaway behavior doesn't solve anything. This conflict is still being fought. ".
The Nancy Court of Appeal confirmed that the French Prime Minister approved his extradition to the US on February 15, 2023.
Following a report by Bulgarian investigative journalists, speculation that Miss Ignatova may have been murdered has grown in recent months. They stated on Twitter that Interpol-wanted Krasimir Kamenov was the source for their information.
After Mr. Kamenov was fatally shot in his home in Cape Town last month, the murder was connected to Miss Ignatova's disappearance by the media. The day after the murder, a US judge ordered Miss Ignatova's brother, who was also under house arrest, to receive "mental health evaluation/treatment.".
After entering a guilty plea to his involvement in the OneCoin scam in 2019, Konstanin Ignatov is now working with the FBI.