By Sabrina Valle

RIO DE JANEIRO (Reuters) - Brazilian police expanded a long-running corruption probe at state-controlled oil company Petroleo Brasileiro SA based in part on secret recordings made by a former executive of Swiss trading firm Vitol SA, according to court documents released on Tuesday.

Police on Tuesday served warrants seeking documents from six people and two companies as part of what is known as the Car Wash investigation into bribery to win contracts to buy and resell Petrobras fuel.

Petrobras said in an e-mailed response it only learned of Tuesday's warrants after the police operation was made public. Petrobras said it was a victim of corrupt employees and that it has cooperated with authorities, providing information that led to the search warrants.

Vitol declined to comment on Tuesday. In the past, it has said it has a zero tolerance policy for bribery and corruption.

Prosecutors have alleged at least 12 million reais ($2.14 million) were paid between 2005 and 2015 to Petrobras employees working in Houston, London and Singapore.

The search warrants were approved by Judge Gabriela Hardt, based in part on tape recordings and other information provided by Marcio Dutra Goncalves, a former Vitol executive in Brazil, Hardt wrote in authorizing the warrants.

"Documentation submitted by Marcio Dutra, together with his collaborative statements, indicates that privileged information were shared at least between 24/10/2005 and 26/11/2014, and would contain the schedule and details of import and export operations by Petrobras," the judge wrote.

Dutra, who was Vitol's Brazil chief executive for about a decade starting in 2005, is cooperating with prosecutors in exchange for leniency, the court said.

He has provided emails, bank records and hundreds of hours of conversations recorded using hidden devices, court documents showed. Dutra recorded the conversations to aid his recollection of events, a person close to the investigation said.

Eight audio recordings attached to the court documents contain conversations with former Vitol executives that approved payments to Petrobras employees, prosecutors said.

Dutra paid up to 12,000 reais in cash a month to a Petrobras employee named Ricardo Brandao for information on Petrobras strategy and pricing that would give Vitol an advantage over competitors, according to the court filings. He occasionally used his own money and was later reimbursed by Vitol through intermediaries, the filings said.

Dutra did not respond to messages left on a mobile phone or email included in court documents. His lawyer, Guilherme San Juan, could not be reached for comment after working hours. Reuters could not establish the whereabouts of Brandao or identify his attorney.