Former Brazilian oil and mining tycoon Eike Batista has been transferred to a high security prison in Rio de Janeiro after being arrested on arrival from New York.
Once Brazil's richest man, he has been accused of paying millions of dollars in bribes to secure contracts with Rio's state government.
Mr Batista has denied any wrongdoing.
He has promised to help the authorities in their efforts to tackle corruption which he says is widespread in Brazil.
Before boarding the plane and turning himself in to police, Mr Batista said he was returning to Brazil to clear his name.
"I'm at the disposal of the courts," he told O Globo newspaper in New York. "As a Brazilian, I am doing my duty."
Under Brazilian law, Mr Batista would have been sent to a special prison wing if he had a university degree.
But as he dropped out before finishing his engineering degree in Germany, he will be serving time in an ordinary cell with six other inmates at the Bangu penitentiary.
Many Brazilian jails are overcrowded and controlled by criminal gangs.
The authorities in Rio say, however, that is not the case at Bangu.
Mr Batista was met by police as he landed in Rio on Monday morning.
He was escorted off the plane and initially taken to the Ary Franco prison in Rio.
After undergoing medical exams and having his hair cut short, he was transferred to the high security prison in the outskirts of the city.
Mr Batista was declared a fugitive by Brazilian officials after police raided his estate in Rio de Janeiro last week and found he had left for New York just hours earlier.
BBC South America business correspondent Daniel Gallas says there was much speculation on whether Mr Batista would return to Brazil or use his German passport to flee to Europe.
Who is Eike Batista?
- Seen by many as the face of Brazilian capitalism
- Bold, extravagant and charismatic, he made most of his fortune during the commodities boom that brought great wealth to Brazil
- Listed in 2012 by Forbes Magazine as the world's seventh-richest man, with an estimated fortune of $35bn
- His Grupo EBX conglomerate spanned mining, oil, shipbuilding and logistics
- After EBX collapsed following a crash in demand for commodities, his wealth slumped to under $1bn (£800m)
But Mr Batista said the trip to New York was not an attempt on his part to flee justice.
He is now due to be questioned about his alleged involvement in a corruption ring involving powerful business people and influential politicians in Rio de Janeiro state.
Investigators accuse Mr Batista of paying the then-governor of the state, Sergio Cabral, $16.5m (£13.2m) in bribes to win government contracts.
Mr Cabral was arrested in November as part of a larger corruption investigation dubbed Operation Car Wash.
As a result of Operation Car Wash, more than 100 people, including Brazil's most powerful building tycoon, Marcelo Odebrecht, have been convicted of crimes such as bribery, racketeering and money-laundering.