Police in the Spanish capital, Madrid, are investigating the death on Sunday of Juan Carlos Márquez, a former executive at Venezuela’s state-run oil company PDVSA.
Mr Márquez, 48, had appeared in court on Friday over his alleged involvement in a money-laundering scheme.
While he denied the allegations of money-laundering, he had reportedly agreed to collaborate with an investigation into corruption at PDVSA.
He was due back in court on Monday.
Police said Mr Márquez had been found hanged in a flat on the outskirts of Madrid.
Low profile, good connections
Mr Márquez was an executive at PDVSA from 2003 to 2014, when the oil company was at the heart of Venezuela’s economy.
While he is widely considered to have been an influential figure in the company with close links to PDVSA’s president at the time, Rafael Ramírez, Mr Márquez kept a low profile and rarely appeared in the media.
He was arrested at Madrid airport on Thursday after arriving on a flight from the US.
He was taken to court on Friday in connection with an investigation into money laundering allegedly carried out by Socialist politician and former Spanish ambassador to Caracas Raúl Morodo.
Mr Morodo, 84, and his son Alejo are suspected of having laundered €4.5m (£4.1m) between 2008 and 2013, which they deny.
Alejo Morodo was arrested in May along with his wife, his Venezuelan associate and the associate’s wife. Police said they would not detain Raúl Morodo because of his age but ordered him to stay in Spain.
Investigators allege that Alejo Morodo charged PDVSA millions of euros for “legal counsel and business advice” that he said two law firms he had links to would provide. He reportedly diverted some of the money he received into his father’s account.
But the investigators say the two law firms never provided any counsel to the state-oil company and that the contracts were “fictitious”.
Sources close to the investigation told Spanish news agency Efe that Mr Márquez had agreed to collaborate with prosecutors following his arrest on Thursday.
The money-laundering case comes just months after 28 people, including two Venezuelan former deputy ministers, were charged with corruption in Andorra over bribes worth $2.3bn (£1.8bn) the suspects allegedly took from companies in return for lucrative contracts with PDVSA.