Sam Bankman-Fried, former boss of failed cryptocurrency exchange FTX, has arrived by plane in New York from the Bahamas to face fraud charges.
The 30-year-old was extradited on suspicion of committing "one of the biggest financial frauds in US history", US authorities have said.
Mr Bankman-Fried, who denies the allegations, may appear in court later on Thursday morning. Two of his former associates have pleaded guilty to related charges.
FTX co-founder Gary Wang and Caroline Ellison, former head of cryptocurrency trading firm Alameda Research, were both charged with "roles in the frauds that contributed to FTX's collapse
They are both now co-operating with the Southern District of New York, he said in a video as court documents were released.
A lawyer for Mr Wang said his client had accepted responsibility for his actions and took seriously his obligations as a co-operating witness.
Ms Ellison and Mr Wang face separate charges from the US Securities and Exchange Commission (SEC). FTX has filed for bankruptcy, leaving many people unable to withdraw funds.